The immature fruit of the same or similar cultivars is called courgette (in Britain, Iran, Ireland, France, the Netherlands, Singapore, Malaysia and New Zealand) or zucchini (in North America, Japan, Australia, the Czech Republic, Italy, Germany and Austria).

[3] They are a vegetable used in Great Britain and areas with significant British influence, though their popularity is waning in favor of immature summer squash like courgette.

[9][10] Before the introduction of Cucurbita species from the New World, marrow signified the immature, edible fruits of Lagenaria,[citation needed] a cucurbit gourd of African origin widely grown since antiquity for eating when immature and for drying as watertight receptacles when grown to maturity.

However, both in North America (since the 1920s) and in Britain (since the 1960s), thinner-skinned immature marrows have gained popularity due to their tender skin and distinct flavour.

Sudell (1966)[12] does not mention courgettes, although he has a section on "vegetable marrow", noting both trailing (vining) and bush types and saying "cut when young".

[16] Members of the plant family Cucurbitaceae, which includes zucchini, marrows, pumpkins and cucumbers, can contain toxins called cucurbitacins.

Also, dry weather conditions or irregular watering can stress the plant and favour the production of the toxin, which is not destroyed by cooking.

Agatha Christie's detective Hercule Poirot often expresses his desire to retire and grow marrows, accomplishing his dream briefly in The Murder of Roger Ackroyd.