Define Ignition Temperature?

Hint: Have you wonder why we need to give spark or any other form of energy to light up the substance.

Complete answer:
Ignition Temperature is the minimum temperature required by the substance to burn or catch fire.
Burning or Combustion (scientifically known) is a spontaneous and exothermic process. Spontaneity is due to the fact that it is exothermic in nature (i.e heat is released during the process). We provide energy to the substance just to start the process and combustion will occur until the whole substance undergoes combustion.
Combustion is dependent on various factors such as nature of substance, amount of oxygen present as combustion takes place in the presence of oxygen, surface area of substance etc.
From the nature of nature it refers whether the substance is flammable or non-flammable . Flammable substances are those which easily burn up these kinds of substances known as combustible substances whereas in case of non-flammable substance it doesn’t catch fire or burns up.
Amount of oxygen is an important parameter as it enables how efficiently the substance or combustible material undergoes combustion. Since combustion is an exothermic process( i.e heat is released ) and today we use a variety of fuels and by burning them we generate energy . So then this parameter comes into picture is how efficiently a substance is given an amount of oxygen level.
Third parameter is surface area from which we refer to the area that is exposed or contact with oxygen. More the contact faster the substance combustion process occurs.

Note:
Like an ignition temperature there is another term Flash point. It is the lowest temperature at which vapors of combustible substances start ignition.