.align directive proper usage with .align(5) and 0x90

.align directive proper usage with .align(5) and 0x90

I am attempting to learn some assembly programming.I came across this
code.The macro ENTRY used in the asm file.But I cannot understand what
this code actually means?.
#define ALIGN(log) .align(log) ,0x90;
what does 0x90 mean? I am quite new to assembly.and why is ALIGN(5) used
instead of typical ALIGN(4) or ALIGN(8)
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) ||
defined(__OpenBSD__)
# define ALIGN_LOG