From TF2 Wiki
The DeathCam is a gameplay feature whereby the in-game camera responds to your death. When you are killed, the camera zooms in on your killer and freezes for several seconds, displaying their name, health, (if they are killed before the freeze, they are titled 'the late',) location, and whether or not they are your nemesis. Their currently equipped unlockable weapon or hat may also be displayed in its own tab. If they have chosen this moment to taunt you (G by default), you will see them gloating over your demise. You may even be able to hear your opponent's taunts and jeers. Some achievements may require you to taunt over the body of a fallen opponent.
In addition to this, an 'On the bright side:' box may be displayed detailing information regarding how your stats measured up to your personal records in that round. Another box will show the level, name and stats of your killer's unlockable weapon should they be wielding one. During the freeze-frame sequence, you may wish to take a screenshot (F5 by default), which will be accompanied by a flash and the sound of a camera shutter. The screenshots are located in (folders prior to Steam main folder)/Steam/steamapps/*steamname*/team fortress 2/tf/screenshots. If you were gibbed by an opponent, your body parts are marked with humorous labels such as "Your Arm", "Your Head", "A Part of You", or "Another Part of You".
The Deathcam can be useful for discerning the location of your killer, allowing you to adapt your strategy if he is still in that area when you respawn.