Chi is the secondary resource common to all three monk specializations in Mists of Pandaria. It is conceptually most similar to paladins' holy power, as a stored 4-point pool. Through his level 30 talents, a monk can choose to buff chi generation in one of three ways, either increasing the maximum pool size via Ascendance, increasing the rate of generation via Power Strikes, or enabling an ability that can periodically completely refill chi (Chi Brew). For all monk specializations, chi is required in order to use the majority of abilities.
Before I move on, let's make one thing clear: Chi and combo points (CPs) are very different systems. CPs are stored on a single target; if a rogue or feral switches targets and uses a CP-generating ability, any CPs stored on the previous target are lost. Chi, in comparison, is stored on the monk, making target switches much simpler.
Second, most abilities that consume CP scale with the number of CPs used; for example, a 5-CP Ferocious Bite hits much harder than a 1-CP Ferocious Bite. All of the monk's chi-consuming abilities have a fixed cost, though this may change later in the beta.