Identify unit fractions

Vitor tries to throw a frisbee to Kaylee but instead it lands in the mud. When Kaylee picks up the frisbee she sees that the muddy part and non-muddy part of the frisbee are the same size. The mud covers $1$ of $2$ equal-sized sections of the frisbee. **What fraction of the frisbee is covered in mud?**  [[☃ math-keypad 1]]