It is called V coz it looks like V. the detailed V model is 
shown below.

SRS                          Acceptance testing 
     \                         /
      \                       /
    HLD(High Level Design)   System testing
       \                    /
        \                  / 
       LLD(Low level      Integration testing
             design)     /
         \              /    
          \            Unit Testing
           \          /
            \        /
              Coding
  
There is no such stage for which you wait to start testing. 
testing starts as soon as SRS document is ready. You can 
raise defects that are present in the document. Its called 
verification.

Plz correct me if i'm wrong..

v and v stands for verification and validation

V model difines multipul stages of development along with 
testing stages. in V.Model "V" stands for "verification and 
Validation" thats wat we r calling "V" model

V-n-V stands for Verification and Validation. These two Vs 
are the components of V-model or Vertical Model.

V word is used to describe the model because since it 
follows Development and Testing parallely, top to bottom, 
vertically!!! And if u look into the model diagram, its 
shown in V structure to give a good view for the model and 
its name.

In V-model, the Development and Testing phases goes in-
hand. For every Development phase there is a Testing phase. 
This model is very convenient and easy to adapt for a SDLC.

Based on the V-model, Testing starts from the requirement 
phase itself. So, according to me, there is no other best 
phase where u can start Testing other then starting right 
from Requirement phase. Its always better to prevent the 
defects migrating from the early stage of project then 
finding them at Testing phase and land up in spending lots 
of money rectifying the defect.

On the light side, Defects are our Hero...Without them we 
would have been unemployed ;)