The third type of head size is oversized. Typically this is any tennis racquet head size that is 107 square inches and up. They can even go all the way up to 130 square inches! With the bigger tennis racquet head size you basically have a bigger sweet spot and more room for error so you get more power and you get more forgiveness.
A lot of people would assume this would be a beginner tennis racquet but I don't recommend it to a lot of tennis playing beginners because a lot of athletic beginning tennis players would quickly outgrow this as you develop more of a full tennis racquet swing. You're going to want probably a mid plus tennis racquet so this is really geared more towards an older player that's going to have a short compact racquet swing and a tennis player that will probably never outgrow that.
The second thing I wanted to talk to you about was the string pattern. That is how many strings are in the racquet because that will also affect how it plays.
There's not too many tennis racquets that have less strings then 16 main tennis strings and 19 cross tennis strings. One example is the Wilson Burn 100S which has a lot less crosses. It only has 15 crosses so there's a lot less strings in the racquet and what that gives you mostly and what it's designed for is SPIN! The more space in between the tennis strings will grab the tennis ball and help spin it, also it will give you a little bit more power.
The second type of string pattern is a 18x20 which is a denser tennis racquet head string pattern. That's going to give you more tennis ball control because it has less string and less space between the tennis strings so less bite and less spin but you will get more control. It's typically good if you hit the tennis ball really flat. The most common tennis racquet string pattern is 16 tennis string mains by 19 tennis string crosses. It might vary one or two main or cross strings but that's a good blend of both power, control and spin.
That is why most tennis racquets are 100 square inch head size and a 16x19 string pattern. That is good for really any beginners to advanced tennis players.
Feel free to reach out with any more questions!