This could be considered as a formal; boundary in that it involves promises and rites. There may however be those who are more loosely attached to the group without being actual members . e. g. the spouses or friends of Catholics who occasionally join them in worship or other Catholic activities. There are many sub-categories within the group the clergy, the religious ie. those in holy orders and the layity. These groups too can be subdivide many times.
The first according to hierarchy seminary students and deacons might be said to be in a group of their own committed, but yet not finally committed to full time service. Then come curates, priests, bishops, cardinals and the pope. Among the religious there are also sub-groups, postulants or candidates, novices and those who have taken full vows. There are other sub-groupings according to the order they belong to Benedictines, Franciscans Cistercians and so on.
Each of these orders have their hierarchy too, with priors, abbots, Mother Superiors etc. Catholicism can also be defined by country or race Some South American countries can be defined as Catholic for instance as it is the predominant religion of that place. Then there are situations where a country was once actively Catholic but has now largely rejected that , such as France, but where Catholicism still has a huge influence on thinking and family life. The layity includes a wide spectrum of both belief and practice.
There are those who attend mass several times in a week, always make confession and are also available for church cleaning rotas. Others attend less often , but their beliefs are orthodox. Some attend, but almost under sufferance as they arent sure that they agree with everything the church says. This can be a matter of theology such as belief in transubstantiation, or it could be a matter of practice as when the Pope condemned the use of condoms. Some hardly if ever attend, but would class themselves as Catholic because of that baptism or even communion as a young person.
They now lead very different life styles, but they and those who know them still class them as Catholics, even in the case of those who claim to no longer believe. Unfortunately for them such a situation is often accompanied by guilty feelings, especially if there is family pressure. Where I stand in all this is between me and my conscience. Just blindly accepting everything that is said and done unquestioningly would do away with any idea of real commitment to Christ and his church.