What are ‘tactical’ nuclear weapons? And will they lead to Armageddon?

There is huge concern that Russian leader Vladimir Putin will use a so-called ‘tactical’ nuke in his war on Ukraine. This term has become common currency in the media. But what is a ‘tactical’ nuclear weapon? Is it actually a ‘smaller’ and ‘less powerful’ bomb , what would its impact be, and could it lead to all-out nuclear Armageddon?