Email spam is Unsolicited Bulk Email (UBE).
Unsolicited means that you lack affirmative consent from the recipient. If you found an address on a web page, on a mailing list, or on Usenet, you don't have consent. If you got an address in gift, sale or trade, you don't have consent. If someone gave you an address for a particular purpose (for example, a commercial transaction, information about your products, or after-sales support) you only have consent to use it for that particular purpose. Use for any other purpose requires a new consent.
Bulk means that you sent a substantively similar message to more than 200 addresses a day. A message that differs from recipient to recipient only by details (e.g. the recipient's name, account number, blocks of random words, characters, numbers, or non-rendered text) is the same message. A message that uses different wording to express the same idea is the same message. If you send the same message to 200 different people day after day, it's spam.