What is considered consciousness? Could someone illuminate me in "consciousness"? 

Is it simply the ability to rationalize, analyze and most important concentrate? With or without ego?

Does consciousness dictate who we are?
In Pali Buddhism, 'consciousness' ('vinnana') is the sense awareness or cognition that operates through the six sense organs to facilite: (i) seeing; (ii) hearing; (iii) smelling; (iv) tasting; (v) touching &amp;; (iv) knowing of the mind's internal feelings, perceptions, moods, thoughts, images, etc. 

To use a rough analogy, 'consciousness' can be compared to the mere reflecting of an image by a mirror. Consciousness only 'reflects' sense objects, like a mirror, that is all. Consciousness does not 'think' or 'analyse', just like a mirror does not think or analyse. 

To quote:


  And what is consciousness? These six are classes of consciousness: eye-consciousness, ear-consciousness, nose-consciousness,
  tongue-consciousness, body-consciousness, intellect-consciousness.
  This is called consciousness
  
  SN 12.2


~~~


  Dependent on eye &amp; forms, eye-consciousness arises. 
  
  Dependent on ear &amp; sounds, ear-consciousness arises...
  
  Dependent on nose &amp; aromas, nose-consciousness arises...
  
  Dependent on tongue &amp; flavors, tongue-consciousness arises...
  
  Dependent on body &amp; tactile sensations, body-consciousness arises...
  
  Dependent on intellect (mano) &amp; ideas, intellect-consciousness (mano-vinnana) arises. 
  
  The meeting of the three is sense contact.
  
  MN 18


In Pali Buddhism, the ability to rationalize, analyse &amp; concentrate are other functions of other kinds of mentality (called 'mano', 'nama', 'sankhara khandha', etc). 

Each of these mental functions, be they consciousness ('vinnana'), intellect ('mano') or mental intention ('sankhara khandha'), can operate without ego or self ('atta'). 'Ego' or 'self' is a natural instinctual yet ignorant idea the mind imputes upon conscious experience &amp; mental activity. (If interested, read more here). 

In Buddhism, what 'we' are is a product of the mind's accumulated &amp; conditioned intentions &amp; thinking (sankhara khandha) &amp; thus 'what we are' is essentially unrelated to consciousness itself (even though what 'we' are are thoughts about what the mind is conscious of). 

In short, we are what we 'think' we are. What we think we are is called 'bhava' ('becoming' or 'existence') in Buddhism. To quote:


  The craving that makes for further becoming (bhava) — accompanied by passion &amp; delight, relishing now here &amp; now there — i.e., craving for
  sensual pleasure, craving to be (bhava), craving not to be (vibhava):
  This, friend Visakha, is the origination of self-identification 
  described by the Blessed One.
  
  MN 44


The 'view' or 'belief' ('ditthi') of 'what we are' is what the mind clings or attaches to (rather than what the mind is conscious of). To quote again: 


  There are these five clingings to the aggregates, friend Visakha: clinging to the form (body) aggregate, clinging to the feeling (vedana) aggregate, clinging to the perception (sanna) aggregate, clinging to the fabricating aggregate (sankhara khandha), clinging to the consciousness (vinnana) aggregate. These five clingings to the aggregates
  are the self-identification ('sakkhaya ditthi') described by the Blessed One."
  
  MN 44


For example, a small baby, before its mind/brain is mature enough to develop ideas of "me" &amp; "I", is continually conscious of an image, sound, smell, taste &amp; touch of a certain woman. Then one day, when the mind/brain became mature enough, it started to categorise (label &amp; solidify) those images, sounds, smells, tastes &amp; touches as "my mother". This categorising of "my mother" was the beginning of developing the ideas that dictate what we are or what we think ourselves to be.

To continue the original quote from above so to incorporate the process of thinking:


  Dependent on eye &amp; forms, eye-consciousness arises. The meeting of the three is contact. With contact as a requisite condition, there is
  feeling. What one feels, one perceives (labels in the mind). What one
  perceives, one thinks about. What one thinks about, one objectifies
  
  MN 18


What "we" are, namely, "self-identification", is what the mind thinks &amp; objectifies about.