# Regular

The term regular can mean normal or in accordance with rules. It may refer to:

## Mathematics

There is an extremely large number of unrelated notions of "regularity" in mathematics.

### Probability and statistics

• Regular conditional probability, a concept that has developed to overcome certain difficulties in formally defining conditional probabilities for continuous probability distributions
• Regular stochastic matrix, a stochastic matrix such that all the entries of some power of the matrix are positive

### Topology

• Free regular set, a subset of a topological space that is acted upon disjointly under a given group action
• Regular homotopy
• Regular isotopy in knot theory, the equivalence relation of link diagrams that is generated by using the 2nd and 3rd Reidemeister moves only
• Regular space (or $T_{3}$ ) space, a topological space in which a point and a closed set can be separated by neighborhoods

## Science and social science

• Regular bowel movements, the opposite of constipation
• Regular economy, an economy characterized by an excess demand function whose slope at any equilibrium price vector is non-zero
• Regular moon, a natural satellite that has low eccentricity and a relatively close and prograde orbit
• Regular solutions in chemistry, solutions that diverge from the behavior of an ideal solution only moderately

## Other uses

• Regular customer, a person who visits the same restaurant, pub, store, or transit provider frequently
• Regular (footedness) in boardsports, a stance in which the left foot leads