This mysterious question has been bothering me for such a long time. What are them? They are clearly not a separation of syllables as in English pronunciation. As you can see in the figure, the word ergonomics should be er・go・no・mics in the dictionary if they are a separation of syllables. Finally, I came across the following explanation today, which fully makes sense and cleared my bewilderment away. 
An entry word and its derived forms are divided into syllables by dots: ac·e·tate. In entries such asethyl acetate that consist of two or more words separated by spaces, the words without centered dots are divided into syllables at their own places in the dictionary. Pronunciations are syllabicated as well, for the sake of clarity. Sometimes the syllabication of the pronunciation differs from the syllabication of the entry word because the division of the pronunciation follows phonological rules, while the division of the entry word reflects the established practice of printers and editors in breaking words at the end of a line for ease of reading.