The term shelter has a number of different meanings, depending on its context. Generally speaking, it refers to a place or structure that provides protection from the elements (such as rain or wind) and/or danger (such as predators). This can include physical structures like buildings or tents, but also more informal forms of shelter such as trees or rocks.
In some cases, "shelter" may refer specifically to a place where people who are homeless can find temporary housing or services. It may also be used metaphorically to describe something that provides protection or safety from harm, such as an emotional support system or a secure job.