Phi in the context of "Coordinate axis"

Many local variants of the Greek alphabet were employed in ancient Greece during the archaic and early classical periods, until around 400 BC, when they were replaced by the classical 24-letter alphabet that is the standard today. All forms of the Greek alphabet were originally based on the shared inventory of the 22 symbols of the Phoenician alphabet, with the exception of the letter Samekh, whose Greek counterpart Xi (Ξ) was used only in a subgroup of Greek alphabets, and with the common addition of Upsilon (Υ) for the vowel /u, ū/. The local, so-called epichoric, alphabets differed in many ways: in the use of the consonant symbols Χ, Φ and Ψ; in the use of the innovative long vowel letters (Ω and Η), in the absence or presence of Η in its original consonant function (/h/); in the use or non-use of certain archaic letters (Ϝ = /w/, Ϙ = /k/, Ϻ = /s/); and in many details of the individual shapes of each letter. The system now familiar as the standard 24-letter Greek alphabet was originally the regional variant of the Ionian cities in Anatolia. It was officially adopted in Athens in 403 BC and in most of the rest of the Greek world by the middle of the 4th century BC.

In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine and standardize the position of the points or other geometric elements on a manifold such as Euclidean space. The coordinates are not interchangeable; they are commonly distinguished by their position in an ordered tuple, or by a label, such as in "the x-coordinate". The coordinates are taken to be real numbers in elementary mathematics, but may be complex numbers or elements of a more abstract system such as a commutative ring. The use of a coordinate system allows problems in geometry to be translated into problems about numbers and vice versa; this is the basis of analytic geometry.

In mathematics, a spherical coordinate system specifies a given point in three-dimensional space by using a distance and two angles as its three coordinates. These are

• the radial distance r along the line connecting the point to a fixed point called the origin;
• the polar angle θ between this radial line and a given polar axis; and
• the azimuthal angle φ, which is the angle of rotation of the radial line around the polar axis.

(See graphic regarding the "physics convention".)

The Brotherhood of the Holy Sepulchre, or Holy Community of the All-Holy Sepulchre, is an Eastern Orthodox monastic fraternity guarding the Church of the Holy Sepulchre and other Christian holy places in the Holy Land. It was founded in its present form during the British Mandate in Palestine (1920-1948). Headed by the Greek Orthodox Patriarch of Jerusalem, the brotherhood also administers the Greek Orthodox Church of Jerusalem, such as metropolitans, archbishops, bishops, archimandrites, hieromonks, hierodeacons, and monks.

The brotherhood's symbol is the taphos, a monogram of the Greek letters tau (Τ) and phi (Φ), for the word taphos (τάφος, meaning "sepulchre, grave"). It can be seen on most Greek Orthodox buildings in Jerusalem.