Two sources explaining "signifier and signified" among many on the WWW.
Daniel Chandler
Excerpts
"Nowadays, whilst the basic 'Saussurean' model is commonly adopted, it tends to be a more materialistic model than that of Saussure himself. The signifier is now commonly interpreted as the material (or physical) form of the sign - it is something which can be seen, heard, touched, smelt or tasted. For Saussure, both the signifier and the signified were purely 'psychological' (Saussure 1983, 12, 14-15, 66; Saussure 1974, 12, 15, 65-66). Both were form rather than substance:
A linguistic sign is not a link between a thing and a name, but between a concept and a sound pattern. The sound pattern is not actually a sound; for a sound is something physical. A sound pattern is the hearer's psychological impression of a sound, as given to him by the evidence of his senses. This sound pattern may be called a 'material' element only in that it is the representation of our sensory impressions. The sound pattern may thus be distinguished from the other element associated with it in a linguistic sign. This other element is generally of a more abstract kind: the concept. (Saussure 1983, 66; Saussure 1974, 66)
Saussure was focusing on the linguistic sign (such as a word) and he 'phonocentrically' privileged the spoken word, referring specifically to the image acoustique ('sound-image' or 'sound pattern'), seeing writing as a separate, secondary, dependent but comparable sign system (Saussure 1983, 15, 24-25, 117; Saussure 1974, 15, 16, 23-24, 119). Within the ('separate') system of written signs, a signifier such as the written letter 't' signified a sound in the primary sign system of language (and thus a written word would also signify a sound rather than a concept). Thus for Saussure, writing relates to speech as signifier to signified. Most subsequent theorists who have adopted Saussure's model are content to refer to the form of linguistic signs as either spoken or written. We will return later to the issue of the post-Saussurean 'rematerialization' of the sign.
As for the signified, most commentators who adopt Saussure's model still treat this as a mental construct, although they often note that it may nevertheless refer indirectly to things in the world. Saussure's original model of the sign 'brackets the referent': excluding reference to objects existing in the world. His signified is not to be identified directly with a referent but is a concept in the mind - not a thing but the notion of a thing. Some people may wonder why Saussure's model of the sign refers only to a concept and not to a thing. An observation from the philosopher Susanne Langer (who was not referring to Saussure's theories) may be useful here. Note that like most contemporary commentators, Langer uses the term 'symbol' to refer to the linguistic sign (a term which Saussure himself avoided): 'Symbols are not proxy for their objects but are vehicles for the conception of objects... In talking about things we have conceptions of them, not the things themselves; and it is the conceptions, not the things, that symbols directly mean. Behaviour towards conceptions is what words normally evoke; this is the typical process of thinking'. She adds that 'If I say "Napoleon", you do not bow to the conqueror of Europe as though I had introduced him, but merely think of him' (Langer 1951, 61)."