Low and middle income country (countries)
Lower-middle income country (countries)

Note: formally, LMICs denotes the plural form.

*To avoid confusion (see table and figure below): When referring to LMIC it is important to clarify whether this comprises low AND middle income countries, or only lower-middle income countries according to the four-group categorisation by the World Bank:[1][2]

This image is generated with real data from the World Bank, and as the orange box and question marks clearly demonstrate, it does make a difference whether LMIC* refers to lower-middle or low & middle income countries.

See also: LIC, MIC, HIC, WB