The word
church is used in different ways, and therefore has different meanings. Most often the context will show the reader which meaning is being used. In Acts 15:4, as I read it and understand the context, the word that is translated as "church" is refering to the followers of Jesus the Christ present at that time in Jerusalem. They were not received by a building, but by people. As the sum of all the believers now and through time, the
church IMHO is also refered to as the "body of Christ," the "Bride of Christ" and various other metaphors.
Here are the definitions given by Merriam-Webster
Definition of church
1
: a
building for public and especially Christian worship
2
: the
clergy or officialdom of a religious body the word church … is put for the persons that are ordained for the ministry of the Gospel, that is to say, the clergy— J. Ayliffe
3 often capitalized
: a
body or organization of religious believers: such as
a : the whole body of Christians: the one church is the whole body gathered together from all ages— J. H. Newman
b : denomination: the Presbyterian church
c : congregation: they had appointed elders for them in every church — Acts 14:23 (Revised Standard Version)
4
: a
public divine worship : he goes to church every Sunday
5
: the
clerical profession : have you considered the church as a possible career?
The word can also be an adjectve (church government), or a verb (he was well churched)