Our scanners can receive either the VHF aircraft band (108-137MHz) like the Uniden 75XLT which is ideal if you want to listen to civilian aircraft transmissions or more expensive models allow you to receive both VHF & UHF aircraft band (225-400MHz) like the Icom ICR6 or Uniden 125XLT These scanners can receive military aircraft transmissions as well as civilian.
Both VHF and UHF are short range, line-of-sight radio transmissions which are restricted to a maximum range of about 200 miles due to the curvature of the earth and usually considerably less depending on the surroundings (hills etc). Some scanners can receive the HF (short wave) aircraft band in addition to the VHF and UHF aircraft bands. The HF band is not restricted to line-of-sight radio transmissions and can be used to monitor Shanwick and the trans-Atlantic routes etc. There are also multi-band scanners which cover much more than just the aircraft bands