Chris Chi asserts that seven stars refers to seven points of the body – head, shoulder, elbow, hand, hip, knee, foot – each can be used to deflect or strike.
Alas, Chris Chi doesn't provide a graphic, and the seven star stance in my tai chi form is quite unlike the seven star mantis stance shown if I google for seven star stance.
(Attempts to include links failed badly).
martialarts.stackexchange.com/users/457/Mark C. Wallace
Chinese martial arts are generally known for assigning flowery names to it's various postures, techniques and excercises.
While quite often the names are similar across styles and lineages, their actual meaning is subject to the particular style, lineage or school.
From this web site (I could not find more authoritative web reference at the moment): The seven brightest stars of the constellation are Ursa Major, the Great Bear, also called the Big Dipper.
In Eastern Asia, these stars compose the Northern Dipper.
They are colloquially named "The Seven Stars of the Northern Dipper" (Chinese: 北斗七星; pinyin: běidǒu qīxīng).
Taoist believe that this star constellation is the seat of the celestial bureaucracy of the gods.
Essentially, Seven Stars is a term that has it's root in Chinese Taoist symbolism.
In martial arts context, this can mean almost anything and it usually varies from lineage to lineage.
This is very well illustrated by the variety of interpretations of the term Seven stars in the answers given to this question.
In conclusion.
If you want to know, what Seven stars refers to in a particular martial art, you must ask the practitioner of that art.
martialarts.stackexchange.com/users/424/Roland Tepp
I found in "Tai Chi Postures & Internal Power Enhancement Taijiquan Shi" by Xu Yu-Sheng another explanation (page 107): The seven stars [the seven joints of the upper torso] unite as one, ant the intent of KUA forms within.
Qi resides and settles below; the seven above rise without effort to embrace complete roundness.
That means that the seven are the two shoulders, the two elbows, the two wrists and the neck.
There is another intriguing drawing of a carriage (4 corners) and three attendants (two carring the carriage and one holding a lantern to beckon the way, in total 7.
Nice, isn't it?
martialarts.stackexchange.com/users/9178/37Friends
'Step up to seven star' in Qigong sense refers to seven Qi-input points in the body.
The locations are: one on top of head, two on each shoulders, two near the waist lines and two back of the hips.
Please be aware to do that it must be done without any tension.
In fighting aspects there are many applications: these could be devastating strikes to the ST9 points.
ST9 points is 'dimmak' points; slap bang in front of the neck, parallel to one's adam's apple (it's there even if you are a woman).
Literally translated it is STOMACH 9, and no it has got nothing to do with stomach.
There are also elbows strikes in there
etc, your choice based on demand.
martialarts.stackexchange.com/users/3075/Pt20
7 stars step is a partner work method used to train distance, timing, and evasion within the Wu/Yang lineage of Cheng Tin Hung (Hong Kong Tai chi Master who taught Dan Docherty).
7 Stars also refers to a guard posture within the style and to a number of martial methods used by the style.
On top of Wudang mountain there is a 7 stars bell.
There is more to it, but that's a little to be going on with.
martialarts.stackexchange.com/users/3216/Charles Gorrie
This question  asks about a seven star mantis stance.  In the Chen Man Ching Tai Chi form I practice we incorporate a move known as "step up to seven stars".  Clearly there is some concept referenced by both.  Unfortunately a  Google search  provides a plethora of noise and very little signal.  What is "seven star"?
What is "seven star"?
martialarts.stackexchange.com
<tai-chi>
martialarts.stackexchange.com/questions/1560
martialarts.stackexchange.com/users/457/Mark C. Wallace
Chris Chi  asserts that seven stars refers to seven points of the body – head, shoulder, elbow, hand, hip, knee, foot – each can be used to deflect or strike. To find out what  Seven stars  refers to in a particular martial art, you must ask the practitioner of that art. Another explanation is that the seven stars [the seven joints of the upper torso] unite as one, and the intent of KUA forms within. 7 stars step is a partner work method used to train distance, timing, and evasion within the Wu/Yang lineage of Cheng Tin Hung (Hong Kong Tai chi Master who taught Dan Docherty). Seven stars can be used to train distance and timing and has  been defined by  Chris Chi who refers to the seven points of the body, and Xu Yu Sheng who describes it as the seven joints of the upper torso combining as one. 
Seven stars have been defined by various people including Chris Chi who says that it refers to the seven points of the body, and Xu Yu Sheng describes it as the seven joints of the upper torso combining as one.  It can be used to train distance and timing. 