Respec is a term for respecialisation and refers to a game feature that allows players to partially or completely reallocate the points they have spent in various skills, 'talents', or 'attributes'.
How to Respec
Players in Diablo 4 will be able to respec their characters at any point on the game and reset skills on the skill trees. This is achieved by right-clicking on the skill as show below:
How to Refund All Skills
Skills will be able to be reset on a point by point bases or via "Refund All" button at the bottom of the skill trees.
Cost of Respeccing
The only requirement to respec skills is a cost in gold and is dependent on your skill level. The amount of gold players currently hold is indicated in the top left of the skill tree.
As players level, the cost of respecing becomes more expensive. At a certain point, the cost will become very expensive and player may decide that it's better to actually re-roll their character from scratch.
Selecting Skills to Respec
The beauty of the new skill trees is the ability to respec individual skills in the tree including skills around them and pre-requisite skills. Players do not have to reset all their skills points (the option do so is there however).