The ball valve gets its name from your internal construction on the valve itself from aoaltwar's blog

A gate valve utilizes an indoor gate that moves down and up on the stem. The stem is attached to the handle which screws the gate up or down, rasing and lowering the gate valve. The gate valve incorporates a few disadvantages. The biggest dilemma is that over the course of time, the stem which controls the gate may, in most cases will break. This means the gate is stuck set up, plus the water will either be stuck on or stuck off. Another issue is that gate valves are notorious for seizing shut after having a long period of non-use.

If they can be freed up, they are going to usually begin to leak. One thing it is best to keep in mind though, there are numerous areas that still require use of gate valves both before and after the water meter. The reason being that a ball valve will be able to be disconnect very fast with just 25 % turn, whereas a gate valve will not be. In the VERY unlikely event that all the river is running within a house, plus the ball valve is turn off quickly, it can cause a water hammer condition, and MAY create a problem elsewhere. This is extremely unlikely and must not be one factor unless essental to your local authority.

Ball Valve
The ball valve gets its name in the internal construction on the valve itself. The lever is attached with a stainless-steel ball around the inside on the valve. The ball includes a hole drilled through it when the valve is on, water passes with the hole portion, if your lever is turned 90 degrees, the ball turns on the solid side also it closes off of the flow of water.

Ball valves are certainly not well suited for regulating flow. This is because ball valves employ a relatively soft ring-shaped valve seat to generate a tight seal. When they are partially open, pressure is applied only to a portion in the valve seat. This can increase the risk for valve seat to warp minimizing its ability to give a good seal causing it to leak.

Another reason ball valves will not be a good choice for regulating flow is the fact they create turbulence and possible cavitation when used by doing this. Turbulence and cavitation reduce flow rates, increase noise and vibration and may even damage valves and piping.

Gate Valve
A gate valve gets its name through the internal construction too because the gate raises and lowers to open up or close the flow of water check this link. The handle sits with a threaded stem that screws inside and outside as the gate raises and lowers. At the end on the gate is usually a washer which is used to seal over flow of water in the event the gate is fully inside closed position.