Because those observing kashrut cannot eat meat and dairy foods together, this means that a meal is either a meat meal or a dairy meal (or a meal for that matter).
You cannot even have meat and dairy at the same table; that is, one person can’t eat a bagel with cream cheese at the same table where someone is eating fried chicken.
To clarify further, you can’t have a piece of steak on one plate, prepared without any dairy, then turn to a second plate and chomp down on a piece of cheese, even if you’ve swallowed the steak.
To ensure that meat and milk not be eaten together in any way, it is customary to wait a certain amount of time between meals. After eating meat, the wait time varies, but the generally accepted amount of time to wait is six hours.
With dairy foods, the wait time between dairy and meat is minimal. This is based on [the talmudic tractate] Chullin 105a, where it says, “How long must one wait between cheese and flesh? And he replied, Nothing at all.”
Still, you should eat something like bread to effectively wipe your mouth of any milky taste, and you should rinse your mouth and wash your hands.
Hard cheese, described as cheese that has aged over six months, such as Swiss cheese, has a stronger flavor and is thought to leave a fatty residue, so it requires a six-hour wait.