their 
/ˈðeɚ, ðɚ/ adjective
always used before a noun possessive form of they /ˈðeɚ, ðɚ/ adjective 1 : relating to or belonging to certain people, animals, or things
▪ All the furniture in their house is brand-new. ▪ They are on friendly terms with their neighbors. ▪ The students are seeking to exercise their rights. ▪ The birds have left their nest. ▪ The trees have all shed their leaves. : made or done by certain people, animals, or things ▪ Their artwork is on display at the museum. ▪ They did their best. ▪ Their conversation went well. ▪ He was angry because of their arriving/being late. 2 : his or her : his : her : its — used to refer to a single person whose sex is not known or specified ▪ Anyone in their right mind would find it unjust. ▪ Each person reacts to their environment differently.
▪ All the furniture in their house is brand-new. ▪ They are on friendly terms with their neighbors. ▪ The students are seeking to exercise their rights. ▪ The birds have left their nest. ▪ The trees have all shed their leaves. : made or done by certain people, animals, or things ▪ Their artwork is on display at the museum. ▪ They did their best. ▪ Their conversation went well. ▪ He was angry because of their arriving/being late.
Do not confuse their with there or they're.
