What does it mean to say that glycolysis is an anaerobic process

It means that it doesn't require oxygen.

Glycolysis is the first step of cellular respiration, which occurs in cytosol. During this process, glucose is broken down into two molecules (with three carbon atoms) called pyruvates, two ATP molecules and one NADH. Glycolysis can be divided into two phases:

• Energy-requiring phase in which two ATP molecules are used

• Energy-releasing phase in which four ATP molecules are made.

Anaerobic glycolysis is performed when amounts of oxygen (O2) are limited. In this type of glycolysis lactate and only two molecules of ATP are produced. Anaerobic glycolysis is effective during intense exercises.