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I'm a 7th grader, and this is what is printed in my Chemistry textbook:
An Acid is a chemical compound that is sour in taste and is soluble in water.
A base is a chemical compound that is bitter in taste.
A salt is a compound that is form alongside water when an Acid and a Base reacts.
Come on. That can't be what Acids and Bases are! What is an Acid, a Base and a Salt?
I will try to make the answer as non-technical as possible, to make it understandable for you.
Some substances are composed of atoms, like $\ce{H}, \ce{O}, \ce{C}, \ce{Fe}$, etc. Each of these atoms actually exist out of even smaller particles, called protons, neutrons and electrons. Protons are positively charged ($+1$), neutrons are, as you might have guessed, neutral, and electrons are negatively charged ($-1$).
The protons and the neutrons are together in the core of the atom, the electrons are in a cloud around it. Because atoms are not charged, an atom has equally many protons as neutrons. A picture will help: (Source: User:Fastfission at Wikipedia)
However, in some cases, those atoms take an extra electron or give a electron to another atom. They are then called ions. For example, a normal natrium atom $\ce{Na}$ has 11 protons and 11 electrons, but a natrium ion $\ce{Na^+}$ has 11 protons and 10 electrons. Similiarly, a normal chloride atom $\ce{Cl}$ has 17 protons and 17 electrons, but a chloride ion $\ce{Cl^-}$ has 17 protons and 18 electrons.
Now we know enough to define what a salt is: A salt is a praticle that is is composed of one or more positively charged ions and one ore more negatively charged ions. For example $\ce{Na^+Cl^-}$, more commonly just written as $\ce{NaCl}$, is common salt, i.e. the kind of salt people do on some of their food (at least in some countries).
There are two special ions, $\ce{H+}$ and $\ce{OH-}$. If you have a liquid, then these two are inside. Now, we call something an acid if there is more $\ce{H+}$ inside than $\ce{OH-}$, and we call something a base if there $\ce{OH-}$ inside than $\ce{H+}$.
I'd also like to note that the book definition is dangerous: An Acid is a chemical compound that is sour in taste. Acids, or chemical compounds in general, are of course not things you should taste to test what they are! They might be poisonous.
