Otoshi refers to all acts in a downward direction. To the dropping movement of your body or arm for example.
In other words, otosu is the principle of downward movement. Therefore, the meaning and – more importantly – feeling, is much more deep then just the Kanji’s translation. Otosu is also an important aspect of internal movement, as you should drop the body internally on impact. This creates heaviness in techniques without having to rely on muscular power.
Otoshi Uke is terminology used to indicated dropping. It is not strictly a specific technique that is referred to.
This movement is from Wanshu. 'Block' down with the palm of the hand in a pressing manner (not pulling).
From Pinan Nidan, with emphasis on using the bottom of the fist.
You can use the palm of the hand if you want to grab right away, or the arm in general.
Absorb the attack on roll on top of it. This way is exceptionally good in combination with techniques like Uraken.