Lacus Felicitatis is a small patch of the lunar

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 surface that has been inundated by flows of lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

, leaving a level patch with a lower albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 than the surrounding ground. It is located in Terra Nivium

Terra Nivium

Terra Nivium is a roughly triangular highland region on the Moon. In his Almagestum novum, the notable selenographer Giovanni Riccioli named the various highland regions terrae...

, an area of continental ground to the north of the Mare Vaporum

Mare Vaporum

Mare Vaporum is a lunar mare located between the southwest rim of Mare Serenitatis and the southeast rim of Mare Imbrium. The lunar material surrounding the mare is from the Lower Imbrian epoch, and the mare material is from the Eratosthenian epoch. The mare lies in an old basin or crater that is...

. About 70-80 km to the northeast of this area are the Montes Haemus

Montes Haemus

Montes Haemus is a curving range of mountains that forms the southwestern edge of the Mare Serenitatis basin on the Moon. They form a less prominent mirror image of the Montes Apenninus range to the west, and curve up to nearly join at the northern end. The eastern edge terminates with the...

, along the southwestern edge of the Mare Serenitatis

Mare Serenitatis

Mare Serenitatis is a lunar mare that sits just to the east of Mare Imbrium on the Moon.It is located within the Serenitatis basin, which is of the Nectarian epoch. The material surrounding the mare is of the Lower Imbrian epoch, while the mare material is of the Upper Imbrian epoch...

.

The selenographic

Selenographic coordinates

Selenographic coordinates are used to refer to locations on the surface of Earth's moon. Any position on the lunar surface can be referenced by specifying two numerical values, which are comparable to the latitude and longitude of Earth...

 coordinates of the Lacus Felicitatis are 19.0° N, 5.0° E, and it has a maximum extent of 90 km. In outline it has a bent shape, with a wing to the northwest and another to the east. The border is somewhat uneven, and it is surrounded by rugged lunar surface.

Three tiny craters within this formation have been assigned names by the IAU

International Astronomical Union

The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

. These are listed below.

Crater	Coordinates	Diameter	Name source
Dag	18.7ºN 5.3ºE	0.5 km	Scandinavian masculine name
Ina	18.6ºN 5.3ºE	3 km	Latin Latin Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...  feminine name
Osama	18.6ºN 5.2ºE	0.5 km	Arabic Arabic language Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book... masculine name

Ina is a semi-circular depression that is only about 30 m deep and is difficult to image from the Earth.

In November 2006, it was suggested that Ina was the result of a gas eruption in the last 10 million years.