What Is Meant By Bolting?

The term "bolting" refers to the growth of an elongated stalk, which has flowers growing from within the main stem.

Some examples of where this happens include cabbage, lettuce, spinach, and other leafy green plants that are grown for their  leaves.

It also applies to some of the brassicas that are grown for their flowers such as broccoli and cauliflower that send up flowering stalks too early thus producing heads that are smaller than usual due to the plant not having matured sufficiently to produce a good sized crop.

Bolting normally happens in hot weather.  It is an attempt by the plant to procreate due to the elongated stalk containing flowers that full of pollen and seeds.  It gives the plant a bitter taste so is considered undesirable by those that grow plants commercially although there are some prefer the bitter taste.