Observation; to watch or examine something carefully, often with an objective or scientific approach (can be used as a verb with 'suru').
子どもの遊び方を観察して、発達段階を調べた。
I observed how the children played to study their developmental stages.
顕微鏡で細胞の変化を観察した。
I observed changes in the cells under a microscope.
よく観察すると、その花には独特の匂いがあることがわかる。
If you look closely, you can tell that the flower has a distinctive scent.