Spelling reform is when people try to change the way we write words so they are easier to understand and learn. It's like when we try to make the alphabet song easier to sing so little kids can learn it better.
Right now, there are a lot of different ways to spell words in English, and it can be really confusing. For example, we spell the sound "ee" in three different ways - "ee," "ea," and "ie" in words like "see," "meat," and "piece." Spelling reform tries to make things more simple by using only one way to spell each sound.
Some people think that spelling reform is a good idea because it would make it easier for people to learn English. But other people think that it would be too hard to change the way we spell words and that it would confuse people who already know how to read and write. So it's a bit of a tricky topic, like trying to decide whether we should learn the old alphabet song or the new one!