Romanization is a way of writing words that use a different alphabet, like Japanese or Russian, using the letters from the Latin alphabet, which is what we use in English.
Basically, it's like putting a different accent on the words so that people who don't speak the language can still read and pronounce them.
Let's say we want to write the word "tokyo" in Japanese. In Japanese, it's written using three characters that don't look like English letters at all.
But if we want someone who doesn't speak Japanese to be able to read it, we can write it using the Latin alphabet like this: "Tōkyō". The accents on top of the "o" show you that the sound is a bit different than an English "o".
Romanization can be really helpful for people who are trying to learn a new language or for situations where you need to write down a word in a language you don't speak.