I hear there's some planks at the back. (6)
I believe the answer is:
lumbar
'at the back' is the definition.
I can't judge whether this defines the answer.
'i hear there's some planks' is the wordplay.
'i hear' becomes 'lumb' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'there's' means one lot of letters go next to another.
'some' says to take the centre.
'planks' becomes 'boards' ('board' can be a synonym of 'plank').
The centre of 'boards' is 'ar'.
'lumb'+'ar'='LUMBAR'
Can you help me to learn more?
(Other definitions for lumbar that I've seen before include "Area of the back between lower ribs and pelvis" , "Near the part of the back between the ribs and the hipbones" , "Area of the back between lowest ribs and pelvis" , "Relating to the lower part of the back" , "Related to lower back" .)