From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Power Items, Z Items, D Items, or Potara (ポタラ, Potara) are powerful tools in the Dragon Ball Z video games. These items can be used to give a character the edge in battle. Whether you need that extra "oomph" or an entirely new moveset, these items provide you with whatever you need for a price.
The best way to become stronger in most Dragon Ball Z video games is by using Power Items. When you gain virtual Zeni, you can buy items to suit your playing style. If you are a player who enjoy using Super Attacks, then perhaps you would enjoy purchasing an item that upgrades your Super Attack damage and make these attacks use less Ki.
These items were originally introduced in the Budokai video game series. In the Budokai Tenkaichi video game series and Raging Blast video game series, Power Items became more exotic. You are able to purchase power ups like the Aura Charge, which gives you different Ki colors and battle powers. In Dragon Ball Z: Tenkaichi Tag Team, some Power Items are able to create Team Player power ups for specific teams. One power-up is called Fusion Kings and allows a Fusion to become even more powerful by giving the fused character an enormous power-up.