Morocco's flag is a red field with a single green five-pointed star at its center, drawn as one continuous interlaced line and known as the Seal of Solomon. The red is older than the star by about 250 years.
A dynasty's color, and a star added in 1915
Red has belonged to the Alaouites, Morocco's ruling family since the 17th century, for as long as the dynasty has existed. Moroccan flags before 1915 were usually plain red banners with nothing on them at all.
The star arrived under the protectorates. France established its protectorate in 1912 and Spain took control of the northern territories, and a plain red banner was no longer distinctive enough to serve as a national symbol. In 1915, during the reign of Sultan Yusef, a royal decree added the green pentagram at the center. The new design carried the dynasty's color forward while marking Morocco out from its neighbors and from the colonial powers, and it declared the country's allegiance to Islam.
The flag has not changed since. It came through the protectorate years and Morocco's independence in 1956 untouched, and legislation after independence confirmed its status.
The Seal of Solomon
A pentagram is a five-pointed star drawn in a single unbroken line. The Seal of Solomon is the particular form of it associated with wisdom and power, and in Islamic culture it carries meanings of wisdom, life, and health. The five points are variously read as the five pillars of Islam or the five senses.
Green is the sacred color of Islam, and on the flag it also refers to the sacred character of the land and to the spiritual values embedded in Moroccan society: love, joy, wisdom, peace, and hope.
Where the flag is flown
The flag is displayed on government buildings and military installations and at national celebrations, most prominently Throne Day on July 30. It is half-masted during national mourning. Military units use variants that add emblems for particular branches or formations.
Beyond official settings, it turns up at cultural festivals, in schools, and at sporting events, and Morocco flies it at international gatherings as a matter of diplomatic routine.
Among other Arab and North African flags
Red and green are common across Arab national flags, and stars are among the most widely used devices in the region, so Morocco's palette is not unusual on its own. What distinguishes the flag is the interlaced pentagram: the Seal of Solomon in this form is Morocco's alone.
The 1915 redesign was itself driven by that need for distinction. Under colonial administration, a national symbol had to be legible against the flags of neighboring territories and of the protecting powers, and the star is what did that work.
References
[1] Morocco's National Flag (https://www.moroccoworldnews.com)
[2] Vexillology Association Resources (http://nava.org)