person The form of a word that shows whether it refers to I or we (first person), to you (second person), or to he, she, it, or they (third person).
number The form of a word that shows whether it refers to one thing (singular: parent) or more than one (plural: parents).
In casual conversation, people often shift between singular and plural or between the third person and the second. In writing, however, such shifts may be confusing.
Note: Also consider how your choice of person suits the tone or approach of your essay. The first or second person, for example, will usually strike a reader as less formal than the third person.