parallel resonant crystal

I don't understand what's the difference btw series resonant crystal
and parallel resonant crystal ?
Are they the same in crystal manafacture ?
In what application I need series one and in what application I need parallel one ?
Thanks for your kindly advice.

All crystals have a series and a parallel resonance. The frequency of one of these is stamped on the case. There are two basic types of oscillator circuits, they operate on the series or the parallel resonance mode.

The manufacturer tries to guess which mode circuit you are going to use when they decide which frequency to stamp on the case. Most logic circuit IC types like microprocessors are short of pins. They use the parallel mode because it uses just one pin. The other lead of the crystal goes to ground outside the IC.

I saw an article which is said:
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"All quartz crystal resonators have a series resonant frequency (fs, frequency of lowest impedance). At this frequency, the crystal appears resistive in the circuit. Crystals can be "pulled" from this series frequency by adding reactance (capacitance) in series with the crystal. When operated in combination with an external load capacitance (CL) the crystal oscillates in a frequency range slightly above its series resonant frequency. This is the parallel (load resonant) frequency. When ordering a parallel crystal, always specify the nominal parallel resonant frequency and the amount of load capacitance in picoFarads (pF). Alternatively, a standard value of CL (such as 20pF) can be ordered; the capacitor values are then calculated to match the crystal CL. Note that a series type will oscillate in a parallel oscillator, and vice versa. The observable difference is a frequency offset of less than + 1000PPM (0.1 %) from the nominal frequency."
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Does it mean I can use the identical crystal for series & parallel resonant
application ? If I want to use the crystal in series resonance mode, just ignore
CL specification because it doesn't matter ?

Thanks for your help.

Each crystal can be used as series or parallel resonant. But the frequency of oscillator can be for 0.1% different as stamped. It is very difficult or impossible to pull such crystal for 0.1% if needed.

I'm still confused about series type & parallel type.
Can someone explain in more details ? or provide some documents ?
Thanks for your help.

flatulent explained it in his third sentence. When we speak of series-parallel type we have a type of oscillator in mind and not the crystal resonances. One type of oscillator can exploit series resonance of crystal and another parallel resonance. Crystal will work in both oscillator types but oscillators frequency will differ for 0.1%.

cryatals are same forall the purposes. it is their use, which depends on user.

Depending on context where the terms series type and parallel type are used it can be interpreted that series type crystal has series resonance frequency stamped and thus it must be used in series resonant oscillator and parallel type crystal in parallel resonant oscillator. In this way you get the same oscillator frequency as stamped on crystal. Thats my guess.

Am I right ?

There is only one type of crystal.
Just depend on how you used it : series resonant mode & parallel resonant mode

In series resonant mode, the specified CL of crystal can be ignored
In parallel resonant mode, CL should be taken care.

Please advise.Thanks.

CL is important with parallel resonant type of crystal one that have parallel resonance frequency stamped and is used in oscillator which exploit parallel resonance of crystal to get precise frequency of oscillation. Frequency is exact when specified CL is used. Series resonance crystals and it's oscillators do not need or use CL. But in both cases, series and parallel, some added reactance is needed to precisely set the frequency of oscillator. This reactance is connected to crystal in series or parallel.