the definition of the word "equation" in math Google give the following definition of the word "equation": 
"In mathematics, an equation is a statement of an equality containing one or more variables. Solving the equation consists of determining which values of the variables make the equality true."
Is really an "equation" is a statement? I think that it more close to a "predicate". I will be happy if someone can give an exact (but still simple) definition of the term "equation"  
P.s. In all cases, I mean equation with unknown(s), not equal. 
Thanks! 

I don't like Google's definition. It's much too narrow for serious mathematics.
Dealing formally with statements of the form
$$
P = Q
$$
is subtle. I won't go into it here. (But do read Barry Mazur's When
is one thing equal to some other thing, as @Shaun suggests.)
Informally, an equation (in mathematics) is a statement that asserts that two mathematical objects are the same. So
$$
1 + 1 = 2
$$
is an equation. The left member is another way to write the number $2$, not an instruction to add $1$ and $1$.
The equation
$$
1 + x = 2
$$
says those two expressions describe the same number. It's implicitly a suggestion that you should "solve for $x$" - find the numerical values (if any) that make the assertion true. That's Google's sense.
Sometimes equations are appear in definitions: we can specify $f$ as the function given by the equation
$$
f(x) = 1 + x
$$
for real numbers $x$.
