There are two tiers of isolation precautions to prevent transmission of infectious agents, Standard Precautions and Transmission-Based Precautions.
Standard Precautions are adopted for all types of patient care. It relies on common sense practices and appropriate use of PPE to prevent infection spreading from patient to staff, other patients and the environment. Risk assessment should be exercised theoretically in every encounter, though with experience and training the step can be carried out in a very short time.
Transmission-based precautions are additionally adopted on top of standard precautions to prevent the spread of infective agents through specific routes of transmission. They include contact, droplet and airborne routes. Contact transmission is by the name spread by direct or indirect contact, especially when we do not take necessary PPE and practice our hand hygiene. Droplet transmission is spread by small droplet nuclei > 5 um in diameter which can travel in air through a short distance (usually 1 m or 3 feet). Airborne transmission involves microscopic droplet nuclei <5 um in diameter which allows them to suspend in the air for extended period of time and travel along with air current to all corners of a room.
Sometimes one infective agent can have more than one route of transmission, e.g. influenza is spread by both droplet (sneezing, coughing) and contact (contaminated environment and fomite).