Speed
A creature has a Speed, which is the distance in feet the creature can cover when it moves on its turn.
Special Speeds. Some creatures have special speeds, such as a Burrow Speed, Climb Speed, Fly Speed, or Swim Speed, each of which is defined in this glossary. If you have more than one speed, choose which one to use when you move; you can switch between the speeds during your move. Whenever you switch, subtract the distance already moved from the new speed. The result determines how much farther you can move. If the result is 0 or less, you can't use the new speed during the current move. For example, if you have a Speed of 30 and a Fly Speed of 40, you could fly 10 feet, walk 10 feet, and leap into the air to fly 20 feet more.
Changes to Your Speeds. If an effect increases or decreases your Speed for a time, any special speed you have increases or decreases by an equal amount for the same duration. For example, if your Speed is reduced to 0 and you have a Climb Speed, your Climb Speed is also reduced to 0. Similarly, if your Speed is halved and you have a Fly Speed, your Fly Speed is also halved.
Burrow Speed
A creature that has a Burrow Speed can use that speed to move through sand, earth, mud, or ice. The creature can't burrow through solid rock unless the creature has a trait that allows it to do so.
Climb Speed
A Climb Speed can be used in place of Speed to traverse a vertical surface without expending the extra movement normally associated with climbing.
Fly Speed
A Fly Speed can be used to travel through the air. While you have a Fly Speed, you can stay aloft until you land, fall, or die.
While flying, you fall if you have the Incapacitated or Prone condition or your Fly Speed is reduced to 0. You can stay aloft in those circumstances if you can hover.
Swim Speed
A Swim Speed can be used to swim without expending the extra movement normally associated with swimming.
Hover
Some creatures can hover, as noted in their stat blocks, and some spells and other effects grant the ability to hover. Hovering while flying prevents you from falling in certain circumstances.