What does “changes” mean in train route?

It's the number of times you have to transfer from one train to another.

Yes, changes mean you have to transfer from one train to another. It appears that there are trains between Venice and Genoa that only have one change at Milan. I also saw one train from Venice to Genoa at 3:50 pm that had no changes.

Thanks so much.

What site are you using for your train information? Some sites have a + sign on the schedule. That will give you the route in detail -- each change, amt of time, etc. Also there are slow trains (making lots of stops) and faster trains making few stops so pay attention to total time. For the tone of your other questions, it could be helpful to spend some extra time with good guidebooks and perhaps some travel videos.

You might find the information on this website useful..it was a great help for me as we don't have train travel near my home.

https://www.seat61.com/Italy-trains.htm

For the best information go to trenitalia.com which is the official site of the National Italian railway. They also have an easy to use app for your devices. When using either one, you must enter the names in Italian (Venezia, Genova). In Venice the main station is Venez S. Lucia but the large station on the mainland is Venezia Mestre. If you are staying in Venice, you’ll want trains from S Lucia.

Sometimes connection with train change is faster than direct. Most train schedules on line are looking for the fastest.

Terminology: A train generally has many stops, at each of which people get on and off. At some of them you may change to another train.
For example, train 1 starts at A, and stops at B, C, D, E, F finally terminating at G.
Train 2 starts at P, and stops at Q, R, S, D, T, U, V, and finally terminates at W
You want to get from B to V. So you get on train 1 at B, travel 2 stops to "D", and change there. Make sure you are quick, as it only stops 2 minutes at each location.
A few minutes later train 2 arrives, you get on and travel 3 stops to V, where you get off.

This is the way trains are designed to work, an interconnecting network.
Unlike planes, which have a huge time penalty for stopping and usually you usually fly from one location to another, trains have little time loss stopping, and travel on fixed routes, with many stops, interchanging with trains on other routes.

Most of the faster train connections from Venezia S. Lucia station to Genova (P. Principe or Brignole stations) only require one change of trains in Milan, although 2 connections may also be suggested at certain times of day. If you're seeing routes with 3 or 4 connections, you may be looking too far in the future. Try dates before June to see typical schedules.