The phrase "certain symmetry" refers to a specific type of balance or similarity in objects, patterns, or relationships. It implies that there is a noticeable or particular level of harmony and equality between different elements. Full definition
Rather, as David finds himself again and again on unexplored sexual terrain, Spa Night illustrates certain symmetries between his parents» experience and his own. (slantmagazine.com)
A «group» is a set of objects, together with an operation, that exhibit certain symmetries — the set of integers and addition, for instance, form a group. (discovermagazine.com)
Only certain symmetries are allowed to be present in a periodically repeating pattern. (scientificamerican.com)