"Mode"
can have a LOT of different meanings. However, because you put this question under "mathematics", Im assuming you want to know more about the mode related to statistics.
Mode is defined as the number that repeats itself the most times in a data set!
Lets say you have a data set [1,2,3,4,5,6,7,8,9]
That data set has no mode, as every number presents itself the same number of times, in this case being 1.
Take this data set: [1,1,2,3,4,5,6,7,8,9]
That data set has a mode of 1. The number "1" presents itself twice in the data set, while every other number presents itself once.
Take this data set [1,1,2,3,4,5,5,6,7,8,9]
That data set has a mode of 1 AND 5. They BOTH repeat themselves TWICE, which every other number only ocurrs once.
If you have any other questions, comment below this answer.
~~~Harsha~~~