This concept is used by Ninian Smart and others to differentiate between the public and overt face of a religion and other aspects of it.

The social and institutional face or dimension of a religion are the public beliefs and attitudes widely held by an entire faith group. These dimensions encompass the faith's dogmas and creeds. They include the officially approved version of what the group believes. They are the officially sanctioned public practices and activities the group engages in.

It is important to differentiate between this-- what we might call collective faith expression--and the interiority of individual religious belief. For example, the Roman Catholic Church acknowledges that individual Catholics are allowed to differ personally from official Church doctrines on the basis of conscience. However, this does not change the institution's adherence to official doctrine.

The social and institutional dimensions of a faith can also differ from how the faith is understood in sacred documents or foundational mythology. For example, while slavery is accepted in the Bible, the most sacred Christian text, no Christian institution in the United States is going to condone or advocate for slavery. Likewise, many mainstream denominations may decide to teach evolution in their private schools while at the same time keeping the creation mythology of Genesis as a foundational text.

This is one of the categories of Ninian Smart's 7 dimensions of religion. It refers to the social institutions of a religion that organizes people's communities and experiences within that religion. This dimension includes organizational structures such as synagogues, temples, churches, covens etc. that retain and pass down the teachings and traditions of that religion.  

Smart's other dimensions include 1) the doctrinal 2) the mythological 3) the ethical 4) the ritual 5) the material and 6) the experiential. He came up with this system of categories in order to offer a systematic approach to studying religions of the world.

If you are operating out of a textbook or some type of class instruction, I would turn to that first.  This might involve defining the term in a more concrete way, and the manner in which you should interpret the concept.  I think that the social dimension of religion refers to how religion is felt and experienced in a particular society.  Essentially, I consider the topic to be asking how a particular society's practices reflect the religion in question.  For example, how do we see the social dimension of Christianity in a particular setting?  In terms of the institutional dimension, I tend to see this as the structure that is in place to ensure the religion's survival.  This can be in the form of temples or churches, as well as the configuration in which the religious issues of the sect of worship can be addressed in a definitive manner.  For example, the institutional dimension for Christianity can be seen as the Vatican and the rule of the papal authority.  These are examples of how I see the social and institutional dimensions of a particular denomination.

The Social and Institutional Dimension: how people's interactions are organized as part of their religion