Question

Difference between three tier and n tier architecture

Answer 1

n-tier implies n is any number - when n=3 then it is the same as n-tier.

The usual definition of 3-tier is presentation, logic & data (in any order), and yes, SOA can confuse the neophyte because sometimes it sits in the data tier, sometimes the logic tier and sometimes both logic & data tiers.

The whole subject is...subjective. If you need some tiers then call it n-tier - if you know that n=7 then call it 7-tier, or n-tier.