Rosetta allows to run (64-bit) Intel apps on Apple silicon by translating the x86_64 instructions.
General documentation about Rosetta from Apple can be found in About the Rosetta Translation Environment.
How does Rosetta 2 work? provides some information how it works under the hood.
Rosetta is difficult to remove because there is no official uninstall method, and because the files installed by Rosetta are protected by SIP (System Integrity Protection) like other macOS system software.
Inofficial instructions how to get rid of Rosetta can be found e.g. here and here, it essentially amounts to
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Getting the file list with
% pkgutil --files com.apple.pkg.RosettaUpdateAuto -
Booting into recovery mode to disable SIP.
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Removing the files.
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Enabling SIP again.
Again: These are inofficial instructions, use at your own risk. I haven’t tested it.
Remark: It is a pity that Apple does not provide a method to remove (or at least disable) Rosetta. I know of a case where some software was inadvertently distributed as an Intel-only package instead of a Universal Binary. This went unnoticed because Rosetta was installed on the computer where the software was tested.