Literally the word minyan ( מִנְיָן) means count or number in Hebrew. A minyan has historically been deemed the necessary number of Jewish men over the age of 13 required to have a religious service. That number being 10. It can be thought of simply as the necessary quorum for the observation of religious activity.
Over time both Reformed and Conservative Judaism now consider women to be able to form a Minyan. Historically in large communities, gathering 10 Jews for worship was not necessarily a challenge but over time as Jewish communities have shrunk for a variety of reasons from persecution to assimilation, assembling the requisite 10 can be a non-trivial task. There were at times members of congregations who were known as ‘Minyan jews’