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.
A spark is a tiny piece of something, usually metal, that is glowing red-hot. Sparks are often made when you strike two surfaces together very hard and bits of one surface are broken off. The sparks in the picture were made by an angle grinder.
Sis forStatic (electricity)
Static electricity is a build up of electrical charge on the surface of something. This charge usually builds up when things rub together. You can make a static charge on a balloon by rubbing it on your clothes, and the child in the picture has got a static charge from sliding down a playground slide.
Static electricity discharges when something with the charge touches something else that can accept the charge. It discharges with a zap that can hurt.
