Activity is defined as human behaviour in terms of what is being done when, during a specified period of time. Whatever an individual spends time on is considered an activity in the time use context.
The ACTUS groups together activities based on the type of time they represent. The types of time used for the ACTUS were proposed by Aas (1982) who identified four types:
1. Necessary time includes activities which serve basic physiological needs such as sleeping, eating, personal care, health and hygiene.
2. Contracted time includes paid work and regular education. Activities within this category have explicit contracts which control the periods of time in which they are performed. These activities, therefore, constrain the distribution of other activities over the rest of the day.
3. Committed time describes activities that a person has committed to because of previous acts or behaviours or community participation such as having children, setting up a household or doing voluntary work. The consequent housework, care of children, shopping or provision of help to others are committed activities. In most cases, services could be bought to provide the same activity. The unpaid work activities which are identified in the satellite national accounts are all committed time activities.
4. Free time is the amount of time left when the previous three types of time have been taken out of a person's day. Many free time activities are considered leisure, but not all. Leisure time is subjective and depends on a particular person's point of view. In fact, many activities included in committed time can be considered to be leisure activities by some people (eg gardening). The only way to obtain more free time is for contracts and commitments to be changed as the total time available in a day is constant.
All activities can be fitted within these four types of time. The order above describes the priority with which the time in a day could be allocated.