Ingress is the act of things or people entering something, or the point where things enter, either literally or figuratively.
The exact opposite is egress: the act of one thing exiting another thing, or the point where things exit, either literally or figuratively.
Part of speech:
sometimes the uncountable kind ("make ingress," "allow ingress," "prevent ingress")
and other times, the countable kind ("the ingress," "this ingress," "these ingresses").
Other forms worth knowing: ingressive, ingressively
How to use it:
This is a formal word with an official, authoritative tone.
Talk about allowing ingress and preventing ingress (or egress), often the ingress (or egress) of certain things or people. That is, you might make sure that certain places or things allow the ingress of air, steam, soldiers, armies, renters, drivers and passengers, pedestrians and vehicles, etc.--or prevent the ingress of mud, moisture, germs, thieves, etc.
You can also talk about ingress into a place or thing (or egress from a place or thing).
And, talk about having or being granted ingress (or egress), making or forcing ingress (or egress), blocking or hampering ingress (or egress), etc.
And to get figurative, we can talk about the ingress (or egress) of a time period, a season, a hope, an idea, etc.
examples: In this skit, Christopher Walken plays a crazy old man who, being interviewed for the Census, claims that a novelty birthday card allows him ingress into Florida.