Some properties of matter change when the size of the sample changes. These are extensive properties—properties that change as the size of the sample changes. Examples of extensive properties are mass, volume, length, and total charge.
Other properties are the same for a substance, no matter the size of the sample—these are intensive properties. An intensive property doesn't change when you take away some of the sample. Examples are temperature, color, hardness, melting point, boiling point, pressure, molecular weight, and density.
Another way of thinking about this is that intensive properties are "internal" to a substance. Because "internal" sounds a little like "intensive," using this nomenclature can help with understanding and differentiating the two concepts.
Flammability is intensive. A little piece of paper will burn. So will a large piece of paper. They will kindle at the same temperature and the reaction will be the same, irregardless of the size of the piece of paper.
The size of the fire, though, depends on how much paper is burnt. The size of the fire is extensive. The more paper you have, the bigger the fire!