Okay, so when we talk, sometimes two words will squish together to make one longer word. This is called synalepha. It's like when you squish two Play-Doh balls together, they become one bigger ball.
Let's try an example. Say we want to say, "I am going to the store."
If we say it really fast and don't pause between the "am" and "going", it sounds like "I'm going to the store." The "am" and "going" squished together to become one longer word.
This happens a lot in languages like Spanish and Italian too. It helps words flow together more smoothly when speaking. So, synalepha is just when two words become one by squishing them together when speaking.