A solid is something in a state that is generally difficult to change the shape of. Most things that you can see around you are solids - your furniture, rocks, and the computer you are reading this on. The other two states that physical things can be in are liquid and gas. Both of these can change shape extremely easily. You can pour water very easily because it is a liquid, but you can't pour a brick.
You do something solo if you do it by yourself, alone. The person in the picture is giving a solo performance.
You solve a puzzle or a problem when you work out an answer or solution. For example, you solve a jigsaw puzzle when you put all the pieces together to make a picture, and you solve a Rubik's cube when you have each face of the cube a single color.
Sis forSomersault
You do a somersault when you sit or squat on the ground and roll over forwards. Some people can do somersaults in mid air, without touching the ground.
