Sight words are the English words you most frequently encounter when reading. They're called sight words because if you learn to recognize them by sight, instead of having to sound them out, it makes reading easier.
This is why they are so important to teach.
When a student learns to recognize sight words automatically, it can increase his or her reading fluency and comprehension. They are useful for young children to know, but also a good idea for struggling readers.
English as an additional, second, or foreign language learners, especially those who are just getting started with reading and writing, will also benefit from studying sight words.
Sometimes you'll find sight words referred to as high-frequency words. That's because they are the most common English words used in writing. Mastering them frees up attention for processing harder and lower frequency words.