In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Shaikh Rabee Bin Haadi [may Allaah preserve him] said:
O youth! O Muslims! It is incumbent upon us to [seek] the knowledge which Muhammad [sallal laahu alayhi wasallam] brought [to mankind and Jinn]. It is incumbent upon all of us – the medical doctor, the engineer and the one who is specialised in the field of chemistry – to take part in [acquiring this knowledge]. We must acquire at least the Fard Ayn, because knowledge is categorised into two categories: Fard Ayn and Fard Kifaayah. It is incumbent upon every individual to acquire that aspect of knowledge which is Fard Ayn.
Marhaban Yaa Taalibal Ilm’ page 100. abridged and slightly paraphrased
Fard Ayn: Obligated on every single person who has reached the age of puberty and is sane [e.g. Tawheed, Salaah etc]
Fard Kifaayah: a communal obligation; but if fulfilled by some, the rest of the people are absolved of responsibility [e.g. funeral prayer etc]