In the Republic of Ireland and the United Kingdom, the P45 is the form that a person is handed when leaving a job. The P45 details income for social security purposes. (The two countries' respective P45s are actually different; it's just that the UK and Ireland have very similar administrative processes here.)

Use of the term "P45" depends on context. See the following examples:
to be given your P45 -- to get fired (possibly unceremoniously)

to ask for your P45 -- to quit your job (possibly unceremoniously and/or defiantly)

to be in possession of your P45 -- to be jobless
(The P45 is handed to the employer when starting at the next job.)
by Jens Ropers July 9, 2004
Pragmatic notification by text, email, phone call to notify someone that their relationship with you is now at an end.
"Did you hear? Peter , the cowardly twunt, issued Linda with a relationship P45 by text!"
"Quick! Get the tissues. She's gonna blow!"
by Eema Braazkumov March 22, 2016
A smal room where 3 to 5 people engage in sexuel or semi-sexuel acts
Person 1:I participated in a p45 yesterday.
by ssammyes August 9, 2018
To be fired in the manner of the 45th President of the United States being fired.
You've been P45'd!
by After1922 March 10, 2021
the smallest road legal car built by the top gear crew(James may,Richard Hammond,Jeremy Clarkson)
person 1: have you seen the peel p45

person 2: yes, i have
by LazarYeeter November 20, 2022
When one is dismissed (sacked) from their employment in the UK
Person 1: Yo is Jason in today?

Person 2: Nah Bob P45'd him yesterday evening!
by Jack Spank9049 February 18, 2023