The basic kickdrum beat of house and techno, consisting of a (usually synthetic) kickdrum on every beat of a bar of 4/4 time.

The legend goes that Giorgio Moroder was wondering how to make the funky music he loved easier to dance to for suburban white kids, when he happened to visit a wedding in Germany. There, he noticed that a large number of elderly Germans were having no trouble at all dancing to the regular bass drum rhythm of the local oompah band. Spotting that this could work for his club audiences too, he started putting the beat on his disco records. The rest was history...

(I have absolutely no evidence for this story, but it's good enough that I want to believe it.)

When applying crude racial generalisations to music, the straight, regimented, four to the floor beat is considered more 'white' than the funky, polyrhythmic breakbeat. However, it's worth bearing in mind that the canonical four to the floor genres - house and techno - were both invented by black people.

One last thing: 4/4 time and four to the floor are not the same thing - virtually all modern dance music is in 4/4, and using the two terms interchangably will cause confusion the first time you tell someone that drum and bass isn't 4/4.