The story
Meraki (μεράκι) came into Greek from Ottoman Turkish merak, a word for desire and enthusiasm, which itself has Arabic roots. The same word spread through the Balkans with different shades. In modern Turkish merak is mostly curiosity, and merak etme means don't worry. In Albanian, merak runs from curiosity to longing, worry and love.
Greek gave it its own colour. Dictionaries list an intense desire, which can tip over into sorrow, and the zeal that drives someone to make a desire real. In the plural, merakia, it can simply mean good spirits. Someone who does things with meraki, and enjoys doing them properly, is a meraklís.
That is the sense the word is known for abroad: putting something of yourself into what you make. It is not reserved for art. A cook can have it, and so can a carpenter or a man who sweeps his front step every morning. What marks it is care beyond what the job strictly needs.
English speakers say someone put their heart or soul into something, which is close. But in English that is a compliment you pay to a result. Meraki describes the way of working, so you can say a meal was cooked with meraki before anyone has tasted it.
Picture a small bakery on Crete just after dawn. The owner shapes each koulouri by hand, though a machine would be faster. Asked why, she shrugs and says something about meraki.