Types:
Buck: Driver uses an inductor to decrease the voltage, input current is less than output current.
Boost: Driver uses an inductor to increase the voltage, input current is larger than output current.
Buck-boost: Driver uses an inductor and can both increase and decrease voltage, some drivers uses linear regulation when decreasing voltage.
Linear: Driver uses a linear chip (like 7135) to reduce the voltage, input current is the same as output current*.
Direct: No current regulation (except resistance) is present, input current is the same as output current*.
All driver types can use pwm for brightness regulation, except for direct all types can also use linear regulation.
*Except for current for the control circuit.
PWM:
Frequency of PWM or switch regulation frequency
The switch regulation frequency will usual depend on voltage, the actual voltage where I measured the frequency can be found at my scope curves in the review.