When playing Texas Hold 'Em you can help narrow down the possible hands a player could have by putting each player into a category based on their playing type. This will help you get an idea of how good your hand is compared to theirs. Here are the main ways to categorise player types:

Tight or Loose?
Tight - A tight player wont play often, and when they do they'll only play strong hands. A tight player will usually win the pot they are playing at the showdown. Most tight players are easy to spot, so the pots they play aren't generally big as other players wont stay in a hand with them.
# Pros - Better cards, Minimal losses
# Cons - Over Predictable, Not much action

Loose - A loose player is unpredictable. They will play many hands and often see the flop with weak cards. They play with the hope that the turn and the river will bring the important cards to give them a strong hand.
# Pros - Lots of action, Unpredictable
# Cons - Big Losses, Unpredictable

Passive or Aggressive?
Aggressive - An aggressive player loves to bet and raise, they will often raise aggressively with a weak hand pre-flop. They like to be in the thick of things are get the pot high.
# Pros - Intimidates other players into folding
# Cons - Requires skill, Can lead to big losses

Passive - A passive player will just call on a hand, rather than bet or raise, they generally don't want to push the bets high even if they have a strong hand, they don't like to be the focus of the attention. They will stay in as long as they are comfortable but as soon as it looks like they might lose they will fold.
# Pros - Gets to play many hands
# Cons - Large losses

Strong or Weak?
Strong - A strong player will have an in-depth knowledge of the game and will make the right decisions at the right time. They are competitive, aggressive and will usually win at the showdown.
# Pros - Competitive and controlled
# Cons - Predictable

Weak - A weak player won't have a good knowledge of the strategies of Texas Hold 'Em and will regularly showdown poor cards.
# Pros - More Fun
# Cons - Large losses
