what does 3G mean?..can i still use my mobile overseas even with out the 3G?...

[MissIndependent]

...is it like tri-band? i need help!? i am a bit confused! i am planning to go overseas soon and didnt want to get a new phone, but consider changing the sim card bought from the country where i am going.. i dont know if my moblike would still work overseas with out 3G.. is it like tri band? i need help!