In what type of reaction or process does heat flow into the system

 The correct answer is:  " endothermic . "

Note:  Heat flows into  [heat may be absorbed within] an "endothermic" reaction or system

          To the contrary, heat flows out  [heat   may exit from or may be released from] an "exothermic" reaction or process.

Hint:  Think of the "prefixes" of:  "endothermic"  and "exothermic" :

  1)  endo- = "within" (as in "endothermic" —heat tends to be absorbed/"within"/"released within"/released within"/into" ;

  2) exo-   = " outwards"/"exit" (as in "exothermic") —heat tends to '"exit"/leave/escape from/"be released out of/form".

Hope this is helpful to you!

Best wishes to you in your academic pursuits

     —and within the "" community"!

it is the most commonly accepted one