90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.
In spoken English, they, them, their, and themselves are used by many people for referring to a person without mentioning whether the person is male or female, especially when referring back to a pronoun such as 'everyone' or 'someone': What happens if someone changes their mind?
In more formal English, 'he or she', 'him or her', or 'himself or herself' are used instead.