I've just encountered this term in the context of a study about sound symbolism, I suppose it is a factor that might play role in how are the new words being formed. What is meant by this factor?
In the context of sound-symbolism and indeed the semiotic theories that are discussed in the article, a sign (linguistic or otherwise) is said to be motivated or iconic if its signifier has something in common with what the sign references.
For example, a picture of a yellow circle with lines around it is typically used to depict the sun. Because it has some visual properties in common with the sun, we can say it is motivated or iconic, whereas the word sun itself has nothing in common with the sun and is therefore said to be unmotivated or arbitrary.
Saussure argued in his seminal Cours de Linguistique Générale that linguistic signs were (mostly) arbitrary, with any apparent motivation the result of coincidences and irrelevant to linguistic theory.
Since then, there has been much debate around this issue, with so called ideophones and phonaesthemes cited as counter-examples to Saussure's views, as well as the discovery of the Bouba Kiki effect.