This is the 211th most frequent Indonesian word.
mantan
"Ex" (referring to a former partner, position, or status).
In this sentence, 'mantan' is used as a noun that refers to an ex-partner, likely in a romantic relationship.
Mantan saya masih sering menghubungi saya.
My ex still often contacts me.
In this usage, 'mantan' functions as an attributive noun describing former affiliation, specifying ex-members of a community.
Sebagian besar pengunjung museum adalah mantan anggota komunitas itu.
Most visitors to the museum are former members of that community.
Here, 'mantan' is used as an adjective to describe someone who used to be in a particular role or position, in this case, a former employee.