Boris gets confused about a line on chart, ... (6)
I believe the answer is:
isobar
'line on chart' is the definition.
(I've seen this before)
'boris gets confused about a' is the wordplay.
'gets confused' indicates an anagram (I've seen 'get confused' mean this (I've seen this in other clues)).
'about' means one lot of letters goes inside another.
'boris' with letters rearranged gives 'isobr'.
'isobr' going around 'a' is 'ISOBAR'.
(Other definitions for isobar that I've seen before include "Line joining places of equal barometric pressure" , "meteorologist's line" , "sign of pressure" , "One showing pressure" , "Weather-map line" .)