Ambiguous characters
There are some examples like that, but it's actually not that common, considering there are thousands of commonly used characters, and there's no name for this too (won't call it a phenomenon either).

熱 &amp; 熟: I remember these words from my childhood. I thought they look so similar at that time. Notice I was a native speaker and already speaking Chinese fluently. This is just a part every Chinese learner must learn, and you will certainly get better at recognizing the differences as time goes on.

Those differences may be in a certain stroke (e.g. one character has an extra stroke 大 &amp; 太, or a difference in length 士 &amp; 土, or a difference in angle/order of strokes 千 干), or there are parts of those characters that are different (e.g. 熱 &amp; 熟).

It might help to learn the basic strokes: https://en.wikipedia.org/wiki/Stroke_(CJKV_character)?oldformat=true#Basic_strokes

Stroke orders matter too. Notice the first strokes of 千 and 干.


check stroke order here: https://www.chineseconverter.com/en/convert/chinese-stroke-order-tool


Here's a list of similar characters if you're interested: http://carlgene.com/blog/2016/06/top-258-most-commonly-confused-chinese-characters/