Elderly men (informal and sometimes disrespectful term); old people or old-timers.
From 'geezer,' possibly derived from British slang 'guiser' or 'guisard' (someone in disguise), or from an alteration of 'geyser' which sounds similar. First appeared in English in the late 1800s as working-class slang.
The origin of 'geezer' is genuinely mysterious—even the best dictionaries are uncertain! It appeared suddenly in British slang around the 1880s and was already a common insult for old men by the early 1900s. Sometimes the best words have the most mysterious origins.
Complete word intelligence in one call. Free tier — 50 lookups/day.