TellA tell is some part of a player's behaviour that enables an opponent, who notices it, to deduce something about a player's style or hand. We divide tells up into concious and inadvertent tells, that is tells from players who act up and know or believe that they're being observed and tells from players who feel unnoticed.
The way a player pushes his chips in in a live game can be a tell. Common and wide-spread among Beginners is the weak-means-strong tell, which occurs when a player tends to always play his stong hands weakly, or always play bluffs strongly. Some players have the habit of always looking up and to the left with an all-in bluff. A further group is known as timing tells, where a player gives away information about his hand by taking a certain amount of time over an action. Equally, a player's demeanour, clothing and manner of speech can also be tells. It's a wide spectrum.