In C#, identifiers are names that you choose to use for things like variables, classes, interfaces, etc.
A keyword is a reserved name that has a specific meaning and that you can’t (generally) use as an identifier.
Here’s the full list of standard keywords in C#:
| abstract | add | as | ascending |
| async | await | base | bool |
| break | by | byte | case |
| catch | char | checked | class |
| const | continue | decimal | default |
| delegate | descending | do | double |
| dynamic | else | enum | equals |
| explicit | extern | false | finally |
| fixed | float | for | foreach |
| from | get | global | goto |
| group | if | implicit | in |
| int | interface | internal | into |
| is | join | let | lock |
| long | namespace | new | null |
| object | on | operator | orderby |
| out | override | params | partial |
| private | protected | public | readonly |
| ref | remove | return | sbyte |
| sealed | select | set | short |
| sizeof | stackalloc | static | string |
| struct | switch | this | throw |
| true | try | typeof | uint |
| ulong | unchecked | unsafe | ushort |
| using | value | var | virtual |
| void | volatile | where | while |
| yield |