* Royal flush: Five cards in sequence and of the same suit, starting from
the Ace down to the 10. Example: A K Q J 10  (Note: A Royal Flush is not a
category of hand in and of itself, it is simply the highest valued
straight flush. Though, since it is mentioned often in the context of hand
rankings, it is worth noting in this list.)
* Straight flush: Any five cards in sequence and of the same
suit. Example: Q J 10 9 8
* Four of a kind: A hand with four cards of the same rank. Example: 4 4 4
4 9
* Full house: A hand with three cards of one rank and two of
another. Example: 8 8 8 K K
* Flush: Five cards of the same suit. Example: K J 8 4 3
* Straight: Five cards in sequence. (The ace can be considered higher than
the king, or lower than the two.) Example: 5 4 3 2 A
* Three of a kind: Three cards of the same rank. Example: 7 7 7 K 2
* Two pair: Two cards of one rank, two of another. Example: A A 8 8 Q
* One pair: Two cards of the same rank. Example: 9 9 A J 4
* No pair: Also known as a high card hand. The following example is
considered "Ace high." Example: A 10 9 5 4

General rules:

Individual cards are ranked - A (high), K, Q, J, 10, 9, 8, 7, 6, 5, 4, 3,
2 (low).
Individual card ranks are often used to evaluate hands that contain no
pairs or other special combinations, or to rank the kickers of otherwise
equal hands. The Ace is ranked low in ace-to-five and ace-to-six lowball
games.

Suits have no value.
The suits of the cards are mainly used in determining whether a hand fits
a certain category (specifically the Flush and Straight Flush hands). In
most variants, if two players have hands that are identical except for
suit, then they are tied and split the pot. Sometimes a ranking called
high card by suit is used for randomly selecting a player to deal.

A hand always consists of five cards.
In games where more than five cards are available to each player, hands
are ranked by choosing some five-card subset according to the rules of the
game, and comparing that five-card hand against the five-card hands of the
other players. Whatever cards remain after choosing the five to be played
are of no consequence in determining the winner. (For example, when
comparing  identical full houses, there are no "kickers".)

Hands are ranked first by category, then by individual card ranks.
That is, even the minimum qualifying hand in a certain category defeats
all hands in all lower categories. The smallest Two pair hand, for
example, defeats all hands with just One pair or No pair. Only between two
hands in the same category are card ranks used to break ties. The highest
single card in each flush or straight is used to break ties (the
Ace-through-five straight is the lowest straight, the Ace being a low card
in this context). Within two Two pair hands, the higher pairs are first
compared. If they tie, then the secondary pairs are compared, and then
finally the kicker.

The order in which cards are dealt is unimportant.
For ease of explanation, hands are shown here neatly arranged, but a poker
hand has the same value no matter what order the cards are received in.