difference between word: and word[:] in for loop

[zowhair]

Hi Friends, I have some confusion in python kindly help me. What is difference between these two statements

 
word = ['xyz', 'dsddf', 'sdfs'] 
for w in word:
    if len(w) > 3:
       word.insert(0, w)

and

word = ['xyz', 'dsddf', 'sdfs']
for w in word:
  if len(w) > 3:
      word.insert(0, w) 

 
for w in word: 

VS

for w in word[:]:

??