A regular verb is any verb whose conjugation follows the typical pattern, or one of the typical patterns, of the language to which it belongs. A verb whose conjugation follows a different pattern is called an irregular verb.
In English, for example, verbs such as play, enter, and like are regular since they form their inflected parts by adding the typical endings -s, -ing and -ed to give forms such as plays, entering, and liked. On the other hand, verbs such as drink, hit and have are irregular since some of their parts are not made according to the typical pattern: drank and drunk (not "drinked"); hit (as past tense and past participle, not "hitted") and has and had (not "haves" and "haved").
The classification of verbs as regular or irregular is to some extent a subjective matter. If some conjugational paradigm in a language is followed by a limited number of verbs, or it requires the specification of more than one principal part, views may differ as to whether the verbs in question should be considered irregular. Most inflectional irregularities arise as a result of series of fairly uniform historical changes so forms that appear to be irregular from a synchronic (contemporary) point of view may be seen as following more regular patterns when the verbs are analyzed from a diachronic (historical linguistic) viewpoint.
