Filtering

The act of drinking an alcoholic beverage through a prostitute's used (and still warm) underwear.

Getting through the traffic with your motorcycle

A person who has no filter tells it how it is while being brutally honest. Others often can't tell if they're being serious or not. They say exactly what's on their mind no matter what the topic is about, or if it's with someone they just met. Honesty to the max, with good intentions.

A term used to describe someone who is very direct when conversing on various subjects. Anyone described as having no filter says exactly what is on his/her mind without cleaning up their language, no matter how offensive or politically incorrect it may be.

When a subject and/or class, usually in higher education scientific fields, is so convoluted and hard to follow, that it is impossible for one to succeed in it. This might be due to the professor, or the subject itself. In this case, the subject acts as a filter, preventing you from moving on to more advanced subjects that built upon it.
This can often extend or apply to specific concepts included or related to a subject or class.
In any of the above cases, it is fair to say that one has been filtered.

When somebody says anything on their mind and don't think about it. Someone who tells like it is and doesn't have a care about other people's feelings and go on about there doing.

When a casual lacks the skill to beat a challenge or boss.