s/he vs they

s/he

• he or she 

they

• People; some people; people in general; someone, excluding the speaker. 

• There (especially as an expletive subject of be). 

• A single person, previously mentioned, but typically not if previously named and identified as male or female, especially if of unknown or (since 21st century) non-binary gender. 

• A group of entities previously mentioned. 

• Their. 

• The, those.