atime
also: access time
The access time (atime) is a file metadata timestamp that records when a file was last read or accessed. It is one of three key modification times tracked by the filesystem.
atime (access time) is automatically updated by the filesystem whenever a file is read, whether through viewing its contents, listing directory entries, or any other read operation. It differs from mtime (modification time, when content changed) and ctime (change time, when metadata changed).
You can view all three timestamps using stat filename or ls -l --full-time filename. For example: stat /etc/passwd shows the exact atime, mtime, and ctime of the file.
Many modern filesystems mount with noatime or relatime options to disable or limit atime updates, since frequent atime writes cause unnecessary disk I/O and wear on SSDs, with minimal practical benefit for most users.