What is the difference between Frequency & Pitch?

[flutestudent]

What is the difference
between the terms Frequency and Pitch? I looked up the encyclopaedia. "It says
Frequency is cycles per second.(measured in terms of Hz). Pitch is something we
perceive, whereas frequency is the physical measurement of vibration. A slight
change in frequency need not mean a change in pitch but a change in pitch
implies a change in frequency." That sounds technical.Can Somebody explain these
to me in layman terms? Last week, I happen to talk to a banjo player, who told
me that all musical instruments are tuned to start at 440 Hz. I didn''t quite
understand what she meant. In a musical orchestra, are all instruments tuned to
the same pitch?...How about the vocalist/the main singer?