1 to greet or acknowledge, but only slightly
2 to express sentiment or mood, but only slightly
Not to be confused with blah the term bleh is generally utilized as a conversation deterrent. Oftentimes people find themselves at the mercy of a conversation they do not wish to participate in. This predicament is typically initiated by a person greeting another or by a person answering a question regarding their general state of health/well being with what might be called a conversation initiator. For example, if person A were to ask person B how he/she is doing, the answer might take the form of an unwanted 30-minute conversation. It is in situations like this, where there is pressure to acquiesce a measure of social etiquette with a response but insufficient time/desire to address the situation with the full answer as would normally be offered that we have use for this term. In definition 1 then the implied sentiment, if transcribed, would be, "I acknowledge that you still exist...that's great...good work...I'd love to take the time to greet you properly but I simply cannot at the moment." (Note: it's possible that, in fact, you would not love to take the time to greet that person properly; in any instance)
Regarding definition 2, intonation is an important variable. Again the same theme of deterring a conversation is at heart, but in the interests of satisfying social etiquette the term may be used with varying intonation to reveal some extra detail as to the person's sentiment/mood. A short descending tone might, for example, reveal anger (another reason why you should not try to have a conversation with that person), while a stretched monotone might be used to express boredom or discontent. With experience this term can come to have a variety of specific meanings when accompanied by a mastery of its applicable intonation.
The uneasy feeling of when you like someone, but when things become real you realise you might not actually like them enough for it to become more than a crush
An adaptation of the word meh, a kind of hybrid between Bleurgh, a sound more than a word, meaning that you are totally disgusted by something, and Meh, a word of passive, unenthusiastic attitude, also meaning whatever. bleh is like a slightly disgusted meh.
person 1: "Oh look, someone just spat their chewing gum out and stuck it under a table."
Person 2: "bleh."