What is E Mail spam exactly?

I'm sure we all want to promote our products and services in the best way we can, and the products and services are USEFUL to everyone
Lets face it 46 million people + in the UK have a mobile phone ,6million + have broadband and most people have a motor car and take a holiday
If we look on the INTERNET can we not make a note of small companies we see there and e mail them about our useful products and services anymore?
There is no way these people can opt in if they haven't seen our websites
Opt out of future mailings they can

I am at the moment trying to embark on an email program for my phones ,in the UK and my on line car site anywhere including the US
The law in the US seems harsh regarding spamming and i would think there will be some sort of outcry from the affiliates merchants as I am led to believe that some 20% of Orange Phones Us sales comes from affiliates

Please help I'm getting more confused by the minute
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Colinm345