What are enplanements?

Some articles on enplanements:

Larsen Bay Airport
... the airport had 2,933 passenger boardings (enplanements) in calendar year 2008, 3,009 enplanements in 2009, and 2,597 in 2010 ... airport (between 2,500 and 10,000 enplanements per year) ...
St. George Airport (Alaska)
... the airport had 604 passenger boardings (enplanements) in calendar year 2008, 610 enplanements in 2009, and 643 in 2010 ... airport (the commercial service category requires at least 2,500 enplanements per year) ...
Akhiok Airport
... Administration records, the airport had 1,220 passenger boardings (enplanements) in calendar year 2008, 1,356 enplanements in 2009, and 1,209 in 2010 ... facility (the commercial service category requires at least 2,500 enplanements per year) ...
Metlakatla Seaplane Base
... records, the airport had 3,344 passenger boardings (enplanements) in calendar year 2008, 3,403 enplanements in 2009, and 4,140 in 2010 ... commercial service airport (between 2,500 and 10,000 enplanements per year) ...
Circle City Airport
... records, the airport had 303 passenger boardings (enplanements) in calendar year 2008, 377 enplanements in 2009, and 355 in 2010 ... airport (the commercial service category requires at least 2,500 enplanements per year) ...