What do determinate, indeterminate, and semi-determinate mean in tomato plants?

Determinate
Determinate means that the plant has limited growth. In this case, the plant forms a flower cluster as its terminal shoot and then expands only sideways, not upward.
 

Indeterminate
In contrast, “indeterminate” means unlimited growth. An indeterminate plant continuously produces new shoots and can therefore keep growing both upward and outward indefinitely.
 

Semi-determinate
These tomato plants have characteristics of both growth types. They initially grow like determinate plants with a limited height, but later continue growing like indeterminate plants and produce fruit over a longer period. They are often a good choice for gardeners who prefer a more compact plant but still want an extended harvest. They can be grown in pots, containers, or in the ground and offer a good balance between size and yield.