A gymslip is a type of dress that is worn by younger girls in school. It is usually a simple dress that goes down to the knees or just above them.
Think of it like a uniform for school that is specifically designed for girls. It's like a dress that is comfortable to move around in and is appropriate for physical activities like sports or gym class.
The name "gymslip" comes from the fact that it was originally created to be worn during gym class. The dress is usually made from lightweight, breathable materials like cotton or polyester, so it doesn't get too hot or uncomfortable during physical activity.
So, if you see a young girl wearing a simple dress to school, it might just be a gymslip!