A double / Tripple bottom is just an opposite formation occurred when prices reverses from almost same level twice or thrice in a falling market. These bottom levels works as an important support levels and this can happen in any time frame whether it is minute chart, hourly chart, daily chart, weekly chart or monthly chart same as tops. Normally, prices when moves up so, creates tops and these tops work as resistance and breaking of these resistance indicates the success of pattern. In double bottom it makes an "W" kind of formation.
For more : learn Full Technical Analysis live