What is the definition of “Avergage Monthly Searches” in Keyword Planner
As defined by Google AdWords here:
Average monthly searches ("Avg. monthly searches"): The average number of times people have searched for the exact keyword based on the location and Search Network targeting that you've selected. We average the number of searches for the term over a 12-month period.
Is the number represented in Average Monthly Searches the number of searches for that specific keyword and the maximum amount of possible clicks to my site?
As implied in the term itself, and definition above, it's an average of searches over a year's time. The number of searches for a specific keyword in Google does not correlate to the number of clicks on a specific site returned in those results, or a "maximum" thereof.
As a starting website, is there a good (minimum) number of monthly searches for a specific keyword that I should be targeting, but that is not overly competitive?
This is really dependent on your search engine marketing strategy. If the keywords you're targeting are highly competitive and your budget is low, then you might find that using less competitive or long tail keywords more effective for conversion to sales, especially for niche websites.
As for a "minimum" number, you certainly want to pick keywords that are being searched for, but might balance this against competition and CPC - again depending on your strategy and budget.
