What is the pipe (|) operator in Linux?

The pipe operator | connects the standard output (stdout) of one command to the standard input (stdin) of the next, creating a processing pipeline. This is the Unix philosophy of composing small, single-purpose tools. Examples: ps aux | grep nginx (filter process list), cat access.log | awk '{print $1}' | sort | uniq -c | sort -rn | head -10 (find the top 10 IP addresses in a web log). Pipes are buffered and run concurrently — the left command produces output as the right command consumes it, making pipelines efficient even on large data streams without loading everything into memory.