Some important definitions related to PLL are as follows :
When PLL is in lock, it can track frequency changes in the incoming signal. The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock range or tracking range of the PLL. It is usually expressed as a percentage of fo, the VCO frequency.
The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. It is also expressed as a percentage of fo.
Pull In Time:
The capture of an input signal does not take place as soon as the signal is applied, but it takes finite time. The total time taken by the PLL to establish lock is called pull in time. This depends on the initial phase and frequency difference between the two signals as well as on the overall loop again and the bandwidth or the low pass filter.