The warmth-and-mud octave
250 Hz sits just below middle C (B3 is 247 Hz) in the octave where almost every instrument overlaps: the low end of vocals, guitar body resonance, piano's left-hand territory, snare drum shell tone, and the upper harmonics of the bass. That crowding is why mix engineers treat 200-400 Hz with suspicion - a little of everything adds up to "mud," and a broad cut around 250 Hz is one of the most common EQ moves in music production.
The same energy read positively is "warmth": cut too much here and mixes turn thin and cold. Learning what 250 Hz sounds like in isolation - this page - is the first step to hearing when a mix has too much or too little of it.
250 Hz in hearing tests
Standard audiometry tests octaves from 250 Hz to 8000 Hz - this tone is the bottom rung of every audiogram. Low-frequency hearing loss (below 500 Hz) is much rarer than high-frequency loss and has different causes, which is why the low frequencies anchor the test.
As a quick self-check, 250 Hz should be clearly and easily audible on any playback device at modest volume - even phone speakers manage it. If it sounds quiet compared to a 1 kHz tone at the same volume setting, that is mostly your ear's natural insensitivity to low frequencies at low listening levels (the equal-loudness effect), not hearing damage.