Participants in interactions (particularly in interactive network media (WWW) aim to change their intentions, goals, decisions and actions - as well as those of other participants in communication. Integrity of information is therefore disturbed; changes are manifested as technical, semantic and social errors and lead to the creation of information, misinformation and disinformation. These become legitimate points of interest in Information Science. Criteria for differentiation among information, misinformation and disinformation are suggested based on their value for different participants in interaction. Therefore, the notion of relevance needs to be redefined and efficiency of information is analyzed from the point of view of participants in the communication process. Usability of information is a measure of efficiency of the information process as judged by the user. Relevance is an accepted term for measuring information usability by the user. Usefulness of information is a measure of sender's efficiency regarding the decision-making processes and actions of the information user. Usefulness is a measure of the actual effect of the author (source) of information on the choice of goals, decisions and actions of the information user.