A suspended computation together with the information needed to evaluate it later. In lazy evaluation by need, forcing a thunk computes and records its result, so subsequent demands can reuse it. Deferral and memoization are distinct: a merely delayed computation need not share its result unless its evaluation mechanism provides that sharing.

Name resolution determined by the nesting of declarations in the source program. An activation of a nested procedure obtains its nonlocal variables from its defining environment, which can differ from the newest activation of the same enclosing procedure when procedural parameters are used.

A variable used within a procedure but declared outside it. Under lexical scope, its binding is determined by enclosing declarations and the associated runtime environment, often accessed through a static chain or programming closure.

A representation of the rest of a computation. In continuation-passing style, a computation receives a function telling it how to use its result. An explicit computer memory argument can be supplied when the continuation is invoked, so capturing control need not capture a snapshot of computer memory.

A mapping from identifiers to their semantic values. A programming closure retains its defining semantic environment; extending it for parameters preserves lexical scope and lets those parameters shadow outer bindings.

A policy under which a running operating-system process keeps the CPU until its current CPU burst ends, it blocks or it voluntarily yields. A newly ready process waits instead of interrupting the current burst.

An operating-system process whose progress is mainly limited by CPU execution, typically with long CPU bursts relative to its input-output waits.

An operating-system process whose progress is mainly limited by input-output rather than useful CPU execution. It often has short CPU bursts separated by blocking waits.

A process algebra in which components communicate through synchronized CSP events. Its operational description uses a labelled transition system; standard observations include CSP traces, CSP stable failures and CSP divergences.^[ref]

A priority queue whose entries have stable identifiers and an auxiliary map from each identifier to its current storage location. An indexed binary heap can therefore support membership and locating an entry in constant time, followed by a key decrease in logarithmic time. Every heap swap must update both affected map entries; otherwise later updates can modify the wrong item.

Formation of an insoluble fraction by acidifying a chemical solution or colloid.

Seizures occurring in the setting of pre-eclampsia that are not better explained by another cause. It is a neurological complication of a systemic pregnancy syndrome, not simply a synonym for high blood pressure.

Following a chain of stored pointers, as in a linked list. A later memory address may depend on the result of an earlier load instruction, limiting how far ahead cache prefetching can run.

Seed dispersal moves seeds away from the plant that produced them. Wind, water, animals and mechanical release can transport seeds; their relative importance depends on seed structure and the environment. Transport is only one step in recruitment: arrival at a site does not guarantee germination or survival.

A winged seed and a seed enclosed in an animal-consumed fruit illustrate contrasting seed dispersal syndromes. A useful experiment compares where marked seeds arrive with where seedlings actually establish, separating movement from later environmental filtering.

Transpiration is loss of water vapour from a plant, chiefly through the stomata of its leaves. Evaporation from internal wet surfaces lowers local water potential, helping draw water through the xylem. Guard cells change stomatal aperture, linking water conservation to entry of carbon dioxide for photosynthesis.

Transpiration and root pressure can drive flow under different conditions. Measuring loss of mass from a watered plant while covering the soil separates much of the loss through its aerial parts from evaporation at the soil surface. Comparing illuminated and dark conditions can test environmental control, while recognising that water loss through the cuticle can persist even when stomata close. Stephen Hales's weighing experiments made water exchange a quantitative problem.^[ref]

Root pressure is positive hydrostatic pressure generated in the root-to-xylem pathway, associated with solute accumulation and water entry. Under suitable conditions it can push sap from a cut plant stem. It can therefore be measured even after the transpiring shoot has been removed.

Stephen Hales attached tubes to cut vines to observe pressure-driven sap rise. This is a different test from weighing a whole plant to measure transpiration: positive pressure from below and evaporation-associated tension from above need not dominate under the same conditions.^[ref]

Nitrogen assimilation incorporates inorganic or organic nitrogen into the compounds of a biological cell. In plants, absorbed nitrate must be reduced before its nitrogen can enter amino acids, whereas ammonium can enter the assimilation pathway more directly. These reactions require energy and carbon-containing precursors, linking nutrient acquisition to photosynthesis and metabolism.

Assimilation differs from nitrogen fixation, which converts atmospheric nitrogen into biologically accessible reduced forms. A plant may assimilate nitrogen supplied by a symbiotic partner without itself catalysing nitrogen fixation.

An axis of a plant bearing leaves at stem nodes, separated by internodes. A rhizome is a specialized plant stem.

An undeveloped shoot or flower, often enclosed by protective leaves.

A modified leaf associated with a flower or inflorescence.