simply put,zikhr is d act of remebrance of Allah(swt)observance of which is voluntary,the conviction of which must be total.zikhr can be observed anywhere,in any position and at anytime.it has neither boundary nor limits.it can be mouthed aloud or expressly silently.the no can be known and counted,and sometimes.it may be deliberately uncounted and therefore unknown.
Like solat,zakat,ramadan,fast and hajj.Allah,The most gracious and merciful ordains zikhr in suratul Ahzab(33)vs 41-42..

However.let it be said dat zikhr is not solat in the instance quoted above.some commentators openly express but was the point being made here.can anyone say that Subhi and Asri prayers are greater in d eyes of Allah than d other three namely Zuhri,Maghrib and isha?Let us check the Glorious Quran,An Nur(24)vs 36-37.
VS 36lit is such a light)in houses which Allah has permitted to be raised to honour:for the celebration in dem,of his name:in dem is He glorified in d mornings nd in d evenings,(again nd again)

V37:By them whom neither trade nor sale can divert 4rm the remembrance of Allah,nor from regular prayer,nor paying zakat,their(only)fear is the day when hearts and eyes will be turned about.
The above ayats solidly highlight d sharp diff btw Remebrance of Allah(zikhr)nd d compulsory daily prayers(salat).it here stresses dat.
".....neither trade nor sales can divert.....".. "but whosever turns away from the remebrance of Allah,indeed he will ave a depressed(difficulty)life and we shall (contd)

(contd) we shall raise him on the day of ressurection blind.(Q20VS124).
Do you care to know that"the example of those who celebrates the praises of Allah to those who do not,is that of living creatures compared to dead ones.?(Hadith)
These are "words on marble"on d importance of zikhr for every man,if you conform,mercy and goodness awaits you,if you reject,....... (Allahu ahlam)..
(Mallam ibrahim ismail baye(nabiyan)..)