Links need to be relevant

Google Senior Webmaster Trends Analyst John Mueller in an office-hours hangout last week was asked this question:

"What matters most? The number of unique referring backlink domains or the total number of backlinks?"

to which he responded:

“We try to understand what is relevant for a website, how much should we weigh these individual links, and the total number of links doesn’t matter at all...there could be one really good link from one website out there that is, for us, a really important sign that we should treat this website as something that is relevant because it has that one link..."

How does Google decide what pages on other websites are relevant to the content of yours and would provide backlinks of high quality?

Google provides a short answer here: www.google.com/search/hows...howsearchworks/algorithms/

which in simple terms says:

• Google starts by analyzing the user's query, and tries to establish the intent behind it.
• The algorithm then uses a language model to determine what strings of words to look up in its index.
• It then tries to determine the category of information the user is looking for.
• The algorithm also tries to determine if the user's intent is to find fresh content only.

Google also provides a VERY long answer here, in the form of a 175-page PDF of its Search Quality Evaluator Guidelines:

www.google.com/search/hows...howsearchworks/algorithms/

Your time would be well spent in studying these guidelines before developing a backlink-hunting plan, to avoid wasting time trying to acquire backlinks that Google will simply ignore.