I have seen these terms in different places, so when a client is requesting a presentation or pitch deck to be delivered, does that mean a Powerpoint file specifically, or it can also imply a PDF?
Unless your client has explicitly specified a format, you're essentially wide open re: what file format you use. That being said, it's usually best to go with something that is widely recognized/supported, so PPT(X) or PDF is likely the way forward. Your client might be confused if they're expecting a PPT(X) and receive an EXE (self-contained slideshow), for instance.
"Presentation" and "Pitch Deck" both mean a slideshow. The most common types are PowerPoint and Google slides, but there are many more presentation programs.
I think a PPT file is clunky as a deliverable; it contains the original, editable slides along with the slideshow, and it takes several steps to start the slideshow. Unless your client wants to be able to do their own edits I would not send a .PPT. I think a multi page .PDF is perfectly acceptable, compact and fool proof.
Pitching the pitch is a whole other story.
IMO this question is too opinionated.
You should ask your client what they want, not ask what the average client wants and blindly aim at that.
For example, what if they want letterboxed images for a customized HTML image caroussel? Neither of the mentioned options in other answers (PPT and PDF) would be ideal; a zip file with JPGs would work best.
Delivery medium is a specification of the assignment and should be discussed beforehand.
If a designer has some doubts about what a term could mean, I am pretty sure a client can, potentially, totally confuse terms.
A client can use a term just to look cool, or because it sounded right. But there is an obligation from the designer's side to clarify what a client really needs, not what he thinks he needs.
A file format depends on specific needs. A PTT is editable if the user has the expected program Powerpoint, but this also can be an old version.
A Pdf is a closed format, which has some advantages, but not all applicable in real life for a client's presentation. It is not foolproof.
But probably he needs to combine different elements on the presentation, for example, a webpage in the middle of an explanation and interact with it, and you either could need a plugin or use an alternative presentation program (Like slide dog)
The client's presentation could just be a bunch of videos paused at will, or could expect awesome motion graphics, he could expect transitions, animations.
He could just use Libre Office and not PowerPoint at all.
He could have another default application to open PDF files, other than Adobe Reader.
So, no. You can NOT imply a PDF is just ok.