Zero is a number. It is represented by the digit "0". If you count things, the result is given as a number. However, if there is nothing to count, one says that the number of things is zero. For example, if one person puts both fists on the table and asks the other how many fingers he has stretched out. Zero is called zero in English, French, Italian and other languages.
Zero has an important meaning in our number system and in mathematics. Let's take the number three hundred and five as an example. If you just put a three and a five, the number is 35, but that's not what it means. We have to put in a zero because the number has zero tens. Every digit has its significance, that is, it has to be in the right place.
Sometimes the zero has a special meaning. For example, the double zero, "00" stands for a toilet. "0 o'clock" means midnight and "year 0" means the beginning of our calendar. To "zero" something means to bring it to the initial setting, and someone who is incapable is also pejoratively called a "zero". The "zero" latitude is the equator and water freezes at 0 degrees Celsius. The lowest temperature that is possible at all is called "absolute zero", it is minus 273 degrees Celsius.