Stasimon

στάσιμος - stasimos

Meaning a "standing still", it referred to the regular songs or odes of the chorus, so named because they were not sung until the chorus had taken their place ready for a dance in the orchestra. Modern scholarship suggests they lined up in a rectangular formation, like a squad of soldiers. in 3 rows of 4 when the chorus was 12 persons and 3 rows of 5 after Sophocles had increased the number to 15, all lined up like a squad of soldiers. 

The stasimon is a section of a Greek play where the chorus sings alone in the orchestra, the actors are off-stage,  It is a section where the chorus describes the background to the story being related, adding details or context, and the setting of the mood.  Often the chorus lament losses and describe feelings of despair.

There is archaeological evidence that the orchestras of the Greek theatres in the 5th century BC were rectangular in design and not circular,

As with all choric odes, the stasimon comprised of pairs of stanzas consisting of a turn or movement called a strophe [in which the chorus moves in one direction, towards the altar] followed by its exact equivalent metrical opposite counterturn or movement called an antistrophe [in which the chorus moves in the opposite direction, away from the altar] . Each pair of turns may or may not be followed by a metrically different "epode". The epode is in a different, but related, metre to the strophe and antistrophe, chanted by the chorus whilst standing still

Hyporchema

A hymn or poem sung by the main body of the chorus, while some of their number accompanied it with mimetic dancing and gesticulation.

Hyporchema - Wikipedia

Reference

Typical Structure of a Greek Play

Naomi A. Weiss (2018). The Music of Tragedy: Performance and Imagination in Euripidean Theater. Univ of California Press. ISBN 978-0-520-29590-2.
Stasimon - Wikipedia

Strophe - Wikipedia
1911 Encyclopædia Britannica/Strophe - Wikisource

Antistrophe - Wikipedia
1911 Encyclopædia Britannica/Antistrophe - Wikisource

Epode - Wikipedia
1911 Encyclopædia Britannica/Epode - Wikisource, the free online library

Prosody (Greek) - Wikipedia

The New Princeton encyclopedia of poetry and poetics- Internet Archive p.1213-  Stasimon

Anne L. Klinck (15 December 2008). Woman's Songs in Ancient Greece. McGill-Queen's Press - MQUP. ISBN 978-0-7735-7721-3.

H. M. Roisman; C. A. E. Luschnig (9 October 2012). Euripides' Electra: A Commentary. 7. Parts of Plays: University of Oklahoma Press. pp. 16–. ISBN 978-0-8061-8630-6.

Francisco Rodríguez Adrados (1975). Festival, Comedy and Tragedy: The Greek Origins of Theatre. Brill Archive. pp. 342–. ISBN 90-04-04313-6.

The Circle and the Tragic Chorus
J. F. Davidson
Greece & Rome
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https://www.jstor.org/stable/643023

To Dance in the Orchestra: A Circular Argument
Author(s): Kathryn Bosher
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Published by: University of Illinois Press
Stable URL: https://www.jstor.org/stable/10.5406/illiclasstud.33-34.0001

Clifford Ashby (1999). Classical Greek Theatre: New Views of an Old Subject. Chapter 3: The Shape of the Orchestra: University of Iowa Press. pp. 24–. ISBN 978-1-58729-463-1.
https://www.jstor.org/stable/j.ctt20q201

The Ephebes' Song: Tragôidia and Polis
John J. Winkler
Representations
No. 11 (Summer, 1985), pp. 26-62
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DOI: 10.2307/2928426
https://www.jstor.org/stable/2928426

The Dramatic Festivals Of Athens : Pickard, Arthur pp. 239-54

Aristotle, Poetics, section 1452b