A solution is a value that satisfies an equation, makes it true. For example, the equation $$x+1=4$$ has the solution $x=3,$ since $3$ is the only value for $x$ that makes the equation true. The solution set for an equation can be everything from zero to infinitely many. The equation $$x=x+1$$ has zero solutions since it's impossible to add $1$ to a value and get the value itself. An equation can also have infinitely many solutions, like $$x+x=2x.$$ It is possible to enter any value for $x$ and the equation will be true.