Can I call the bags in the image above polybag? Is polybag an English word?
I think those bags are made from polypropylene, and that's the source of the word "polybag" - however, that is not at all a common term in Australian English either (following on from @LawrenceC's comment).
Wikipedia gives some alternatives: https://en.wikipedia.org/wiki/Plastic_bag
The most common one is "plastic bag" - though that gives the impression of something much weaker than the one in your picture. I would recommend calling that something more specific like:
- strong plastic bag
- tough plastic bag
Polybag is certainly a commonly used word in British English for a small plastic, usually polythene, bag.
The term is more commonly used for resealable (Ziploc) bags than open bags like those of the picture. However, those in your picture would often be referred to as a polybag.
So, can you call those bags polybags? - Yes.