Mass refers to the amount of matter in any given object. In other words, it is the equivalent of the energy content. In order to convert mass to energy you would use Albert Einstein's formula E = Mc2.
Examples of mass include:
Mercury (3.302 x 1023 kg)
Venus (4.8685 x 1024 kg)
Earth (5.9736 x 1024 kg)
Mars (6.4185 x 1023 kg)
Jupiter (1.899 x 1027 kg)
Saturn (5.6846 x 1026 kg)
Uranus (8.6832 x 1025 kg)
Neptune (1.0243 x 1026 kg)
Mass is anything that takes up space.
Things include;
Beds, chairs, tables, desks, trees, books, land, etc.