What is the following activity known as in vocabulary learning? Find words…

A collocation is a pair or set of words that speakers of a language habitually place together, well beyond what grammar rules alone would predict — a given noun conventionally attracts certain adjectives, verbs, or prepositions purely by the accepted usage of native speakers, not by any grammatical requirement.

Asking learners to find the words that naturally go with 'rain' — such as heavy rain — is a classic collocation-building exercise: it trains students to notice which modifier speakers conventionally attach to a given noun (heavy rain, not strong rain, even though 'strong' is grammatically valid), rather than any word that grammar alone would permit.

• A phrase only names any grammatical grouping of words that functions as one unit (for example, in the rain); it says nothing about which particular words conventionally combine with rain, so it does not capture the activity.

• Word groups is too generic — it can describe any set of words considered together, with no requirement that they habitually co-occur, so it misses the frequency-based pairing the activity targets.

• A word web is a graphic organizer that clusters words sharing a meaning or theme around a central idea; it maps semantic association, not the fixed word-partnering norms this exercise practises.

Since the activity asks learners to identify the conventional partner-words for 'rain', it is an exercise in identifying collocations.