When handling data in KS3 Maths you'll come across two distinct types - quantitative and qualitative. Qualitative data refers to things with no numerical value, such as colours, gender, favourite films etc. Quantitative data is data which can be represented by a number, such as the number of people with red hair, the number of males or females in a school or the number of people who liked the latest Star Wars film.
In addition, there are two types of quantitative data; countable (discrete) and measurable (continuous). Discrete data will always give you a whole number (how many children like apples, for example. You'll never get half a person!). Measurable data may very well give you fractions (how tall is that building? 11.37 metres). Do you see the difference? You need to recognise and know how to deal with these different types of quantitative data.
Try the following quiz to acquaint yourself with discrete and continuous quantitative data. Good luck!