A coincidence is commonly defined as "a remarkable concurrence of events or circumstances without apparent causal connection." And yet there's more to the story.
Since the 3D world requires empirical evidence of a relationship that's verifiable through at least one of our five senses, anything that happens in life without previously planning the interaction is generally devalued as a chance occurrence.
In terms of the awakened individual, there are no chance occurrences...only synchronicities.
These remarkable coincidences are a result of your interaction with the holographic Universe, which is created by you, for you.  These chance encounters, repeating numbers, and overheard prophetic statements are placed there for you to tune into---or not---depending on your thoughts, feelings and vibration at the time.
In essence, coincidences are synchronistic breadcrumbs placed in your path.  It's up to you how much relevance you give it.
And note that ALL moments are coincidences in their truest form.  We tend to assign some moments more relevance than others; this is how we make choices as to which path of breadcrumbs we'll follow.