What is the substitution effect in economics?

Substitution goods are those goods which can be used in
exchange of each other without sacrificing the satisfaction level. On the other hand the
Substitution effect is the effect whereby one good is being effected inversly by another
good.

The idea that as prices rise (or incomes decrease)
consumers will replace more expensive items with less costly alternatives. Conversely,
as the wealth of individuals increases, the opposite tends to be true, as lower-priced
or inferior commodities are eschewed for more expensive, higher-quality goods and
services - this is known as the income effect.