Indeterminate (or ‘cordon’) tomatoes have a growing habit that, given the right conditions, will continue growing almost indefinitely. To keep the plants under control, the side shoots must be regularly removed (‘pinched out’), leaving only the main stem to develop. This, in turn, must be staked or trellised to keep the plant upright and off the ground. 

Generally speaking, indeterminate tomatoes take more work to look after than indeterminate (bush) tomatoes, but they are higher yielding and often better tasting.