From the good folks at wedMD:

The typical ear infection, called otitis media, occurs when a cold or allergy causes swelling of the baby’s eustachian tube, causing blockage that allows bacteria to grow in the middle ear. Otitis media is particularly common in babies because their immune systems are immature and their eustachian tubes may not effectively drain fluid from the middle ear. There are two types of middle ear infections. Acute otitis media often causes pain, fever, and a bulging red eardrum. Otitis media with effusion (OME) occurs when the middle ear doesn’t drain properly and fluid is trapped behind the eardrum.

From our experience yesterday:

Whining, crying, and not cooperating at daycare; holding his ear during playtime and refusing comfort; parents being called twice, until parents confer to change schedules—so one can keep an appointment and the other can worry over making up work; an afternoon doctor’s appointment where the doctor said she’d be crying with this infection; ice cream from Brown Sugar Bakery mostly for the parents (somewhat unrelated); and the blessing of pain killers that taste like strawberry and a ten-days supply of grape-smelling medication (for the boy, of course).