This reduced-rate of £20 is for those from, and still living in, a developing country (for least developed country membership see here) and on a low income. This is an online subscription with access to IBIS online only. No print option.
Qualifying countries see here (DAC List – two right hand columns)
All subscriptions are for the calendar year (Jan-Dec). Those joining from November do so for the remainder of the current year and the next calendar year.