"Leaning" is a term I like to use to describe technical levels defined by consolidated price action in an area, moving averages, trendlines, or Fibonacci retracement. The reason why traders like those levels is because they can define risk and limit risk against those areas. If you can limit risk you stand to only risk a little on your trades. If you are not "risked" or stopped out, you stand to make more than the amount that you risked.
That's the secret of trading. Not being right all the time, but when you are right making more than one you are wrong.
On this video I outlined levels that traders are likely to lean against in the AUDJPY on the daily chart. We don't know what will happen in the future, but we do know that the market to react to the "lean" levels, and that helps to put the odds of success as a trader in your favor.