The variables (features) present in the dataset are independent of each other as per the assumption.
Here the dependence is on a given condition and not on the remaining variables (features) in the data.
The condition can be anything like a month, year, season, etc. but not a feature in the data because it will be constant so it can't be a feature.
e.g What is the probability of getting heads in a coin toss given the coin is a fair coin. Here the condition is the coin being a fair coin and not an unfair coin with the same face on both sides.