Question

When a reaction results in an almost complete conversion of reactants to products, chemists say that the reaction goes to completion?

Answer 1

Yes, that is completion reaction.
This type of reactions do not set up an equilibrium and goes until one of the reactants runs out.
Three major types of completion reactions are:
1. Formation of a slightly ionized product (for example mixture of sodium bromide and potassium chloride).
2. Formation of a gas (for example hydrogen gas from metal and acid).
3. Formation of a precipitate (feor example silver chloride).