What’s this stuff in my mouth?

Lately I’ve been getting these little white bumps in my mouth and one time I scraped one off with my tongue and it resulted in the hole which is circled on the left of the picture. The other circle is an example of one of the holes.
If anyone has any idea of what they could be I really want to know if it’s serious and what it could mean?
What’s this stuff in my mouth?
What’s this stuff in my mouth?
What’s this stuff in my mouth?
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