Definitions

A biennial plant

A flowering plant that takes two years, generally in a temperate climate, to complete its biological life cycle.  In the first year, the plant undergoes primary growth, in which its leaves, stems, and roots (vegetative structures) develop. Usually, the stem of the plant remains short and the leaves are low to the ground, forming arosette. After the first year, the plant enters a period of dormancy for the colder months. During the next spring or summer, the stem of the biennial plant elongates greatly, or "bolts".

Species:

A group of organisms (vegetables) that can reproduce naturally with one another and create fertile offspring

Vegetable: 

Any plant part consumed for food that is not a fruit.   However, since the fruit vegetable group's products are eaten as part of the main meal, the words "fruit" and "vegetable" are mutually exclusive, and tomatoes and others are defined as vegetables in their culinary definition. 

This group of plants produces vegetables from the ovary of their fowers, and hence they are defined as fruiting plants.  However, since the products are eaten as part of the main meal, their culinary definition is vegetables.

Vegetable cultivar:

A subspecies classification describing plants varieties which are produced through artificial selection.
Vegetable variety:

A precisely defined group of vegetable plants, selected from within a species, with a common set of characteristics.

Different forms of the same species are considered varieties.

Determinate tomatoes:

Plants grow 2 to 3 feet tall and provide numerous ripe tomatoes ripening all at once over a brief period, and then they die

Indeterminate tomatoes:

Vines are produced all season long, and then the plants die mid-to late-season but provide fruit all season, giving fruit more evenly throughout the season.

Types of tomatoes:

See "overview" section on tomatoes.