A <em>decimal point</em> is the symbol that is used to make the separation between the whole part and the fractional part of a number. Currently, not only is a point used to separate both parts, but the comma can also be used.
Example:
The number 39.847, in which 39 is the whole number, while 847 is the decimal part where 8 represent tenths, 4 hundredsths, and 7 thousandths.