a portal or entrance (the opening or the closure literally or figuratively)

1. a door

a. the vestibule

b. used of any opening like a door, an entrance, way or passage into

c. in a parable or metaphor

1. the door through which sheep go in and out, the name of him who brings salvation to those who follow his guidance

2. "an open door" is used of the opportunity of doing something

3. the door of the kingdom of heaven (likened to a palace) denotes the conditions which must be complied with in order to be received into the kingdom of God