How to know what the 'errno' means?

How to know what the 'errno' means?

c linux errno

c

Is &errno legal C?

c language-lawyer errno

c

What's the meaning of the %m formatting specifier?

c printf glibc errno format-specifiers

c

Should I set errno?

c errno

c

How to set errno value?

c linux error-handling errno

c

Cannot assign requested address - possible causes?

c sockets tcp errno

c