Mom says my baby brother is teething. What's that?

Teething is when a baby's teeth start to come in. Teething can be tough for babies - and their big brothers and sisters! Teething babies may cry because their gums hurt. Some have trouble sleeping, and some drool a lot.

Are babies born with teeth?
Will my baby sister ever get any teeth?
How many teeth do I have?
Why do baby teeth fall out?
How do my teeth know when to fall out?